From 1861f9a715e508ae7a6f78be02fd23f8b8a7fc2e Mon Sep 17 00:00:00 2001
From: andig <cpuidle@gmail.com>
Date: Wed, 22 Jul 2026 11:26:54 +0200
Subject: [PATCH 1/4] Optimizer: configurable battery efficiency

---
 api/api.go                                 |  5 ++
 api/implement/implementations.go           | 15 ++++++
 cmd/implement/implement.go                 |  1 +
 core/site_optimizer.go                     | 35 +++++++++++--
 core/site_optimizer_test.go                | 28 ++++++++++
 meter/config/config.go                     | 50 ++++++++++++++++++
 meter/config/config_test.go                | 60 ++++++++++++++++++++++
 meter/template_test.go                     | 18 +++++++
 util/templates/defaults.yaml               | 13 +++++
 util/templates/includes/battery-params.tpl |  5 ++
 10 files changed, 227 insertions(+), 3 deletions(-)
 create mode 100644 meter/config/config_test.go

diff --git a/api/api.go b/api/api.go
index 3535b9dc73d..282e511dc5f 100644
--- a/api/api.go
+++ b/api/api.go
@@ -59,6 +59,11 @@ type BatterySocLimiter interface {
 	GetSocLimits() (min, max float64)
 }
 
+// BatteryEfficiency provides the battery charge/discharge efficiency in %
+type BatteryEfficiency interface {
+	GetEfficiency() float64
+}
+
 // MaxACPowerGetter provides max AC power in W
 type MaxACPowerGetter interface {
 	MaxACPower() float64
diff --git a/api/implement/implementations.go b/api/implement/implementations.go
index 610e8b7dfe2..01fe1ff4d06 100644
--- a/api/implement/implementations.go
+++ b/api/implement/implementations.go
@@ -53,6 +53,21 @@ func (i *iBatteryController) SetBatteryMode(p0 api.BatteryMode) error {
 	return i.batteryController0(p0)
 }
 
+func BatteryEfficiency(batteryEfficiency0 func() float64) api.BatteryEfficiency {
+	if batteryEfficiency0 == nil {
+		return nil
+	}
+	return &iBatteryEfficiency{batteryEfficiency0}
+}
+
+type iBatteryEfficiency struct {
+	batteryEfficiency0 func() float64
+}
+
+func (i *iBatteryEfficiency) GetEfficiency() float64 {
+	return i.batteryEfficiency0()
+}
+
 func BatteryPowerLimiter(batteryPowerLimiter0 func() (float64, float64)) api.BatteryPowerLimiter {
 	if batteryPowerLimiter0 == nil {
 		return nil
diff --git a/cmd/implement/implement.go b/cmd/implement/implement.go
index ec034e1f4e1..7c4a596560d 100644
--- a/cmd/implement/implement.go
+++ b/cmd/implement/implement.go
@@ -61,6 +61,7 @@ func generate(out io.Writer) error {
 		reflect.TypeFor[api.Battery](),
 		reflect.TypeFor[api.BatteryCapacity](),
 		reflect.TypeFor[api.BatteryController](),
+		reflect.TypeFor[api.BatteryEfficiency](),
 		reflect.TypeFor[api.BatteryPowerLimiter](),
 		reflect.TypeFor[api.BatterySocLimiter](),
 		reflect.TypeFor[api.ChargeController](),
diff --git a/core/site_optimizer.go b/core/site_optimizer.go
index 85ff2b828f6..75d5e0e832e 100644
--- a/core/site_optimizer.go
+++ b/core/site_optimizer.go
@@ -320,13 +320,15 @@ func (site *Site) optimizerUpdate(battery []types.Measurement) error {
 		ft = prorate(ftSlots, firstSlotDuration)
 	}
 
+	batteryEta := site.batteryEta(battery)
+
 	req := optimizer.OptimizationInput{
 		Strategy: optimizer.OptimizerStrategy{
 			ChargingStrategy:    optimizer.OptimizerStrategyChargingStrategy(site.GetOptimizerChargingStrategy()),
 			DischargingStrategy: optimizer.OptimizerStrategyDischargingStrategyDischargeBeforeImport,
 		},
-		EtaC: eta,
-		EtaD: eta,
+		EtaC: batteryEta,
+		EtaD: batteryEta,
 		TimeSeries: optimizer.TimeSeries{
 			Dt: dt,
 			Gt: prorate(gt, firstSlotDuration),
@@ -337,7 +339,7 @@ func (site *Site) optimizerUpdate(battery []types.Measurement) error {
 	}
 
 	// end of horizon Wh value
-	pa := lo.Min(req.TimeSeries.PN) * eta * 0.99
+	pa := lo.Min(req.TimeSeries.PN) * batteryEta * 0.99
 
 	details := requestDetails{
 		Timestamps: asTimestamps(dt, now),
@@ -659,6 +661,33 @@ func (site *Site) loadpointRequest(lp loadpoint.API, minLen int, firstSlotDurati
 	return bat, detail
 }
 
+// batteryEta returns the capacity-weighted charge/discharge efficiency of the home
+// batteries. Weighted since the optimizer api only accepts a single global value.
+func (site *Site) batteryEta(battery []types.Measurement) float32 {
+	var sum, capacity float64
+
+	for i, dev := range site.batteryMeters {
+		if i >= len(battery) || battery[i].Capacity == nil {
+			continue
+		}
+		c := *battery[i].Capacity
+
+		e := float64(eta)
+		if m, ok := api.Cap[api.BatteryEfficiency](dev.Instance()); ok {
+			e = m.GetEfficiency() / 100
+		}
+
+		sum += e * c
+		capacity += c
+	}
+
+	if capacity == 0 {
+		return eta
+	}
+
+	return float32(sum / capacity)
+}
+
 func (site *Site) batteryRequest(dev config.Device[api.Meter], b types.Measurement, grid api.Rates, minLen int, firstSlotDuration time.Duration) (optimizer.BatteryConfig, batteryDetail) {
 	bat := optimizer.BatteryConfig{
 		CMax:      batteryPower,
diff --git a/core/site_optimizer_test.go b/core/site_optimizer_test.go
index 8b667b7c32c..e9df9b41c4b 100644
--- a/core/site_optimizer_test.go
+++ b/core/site_optimizer_test.go
@@ -322,3 +322,31 @@ func TestCurrentSlotSuggestion(t *testing.T) {
 	// no result yields an empty suggestion
 	assert.Empty(t, currentSlotSuggestion(batteryDetail{Type: batteryTypeBattery}, optimizer.BatteryResult{}, true, false, 1, ""))
 }
+
+type effMeter struct {
+	api.Meter
+}
+
+func (m effMeter) GetEfficiency() float64 {
+	return 100
+}
+
+func TestBatteryEta(t *testing.T) {
+	device := func(m api.Meter) config.Device[api.Meter] {
+		return config.NewStaticDevice(config.Named{}, m)
+	}
+	measurement := func(capacity float64) types.Measurement {
+		return types.Measurement{Capacity: &capacity}
+	}
+
+	// no batteries
+	assert.Equal(t, eta, (&Site{}).batteryEta(nil))
+
+	// unconfigured battery uses the default
+	site := &Site{batteryMeters: []config.Device[api.Meter]{device(nil)}}
+	assert.Equal(t, eta, site.batteryEta([]types.Measurement{measurement(10)}))
+
+	// capacity-weighted average of 100% (10 kWh) and default 90% (30 kWh)
+	site = &Site{batteryMeters: []config.Device[api.Meter]{device(effMeter{}), device(nil)}}
+	assert.InDelta(t, 0.925, site.batteryEta([]types.Measurement{measurement(10), measurement(30)}), 1e-6)
+}
diff --git a/meter/config/config.go b/meter/config/config.go
index d516142350a..45c885299b4 100644
--- a/meter/config/config.go
+++ b/meter/config/config.go
@@ -3,15 +3,22 @@ package config
 import (
 	"context"
 	"fmt"
+	"maps"
 	"strings"
 
 	"github.com/evcc-io/evcc/api"
+	"github.com/evcc-io/evcc/api/implement"
 	"github.com/evcc-io/evcc/util"
 	reg "github.com/evcc-io/evcc/util/registry"
+	"github.com/spf13/cast"
 )
 
 var Registry = reg.New[api.Meter]("meter")
 
+// efficiencyParam is the battery efficiency setting. It is handled here instead of
+// in the device implementations since it is not used by the device itself.
+const efficiencyParam = "efficiency"
+
 // NewFromConfig creates meter from configuration
 func NewFromConfig(ctx context.Context, typ string, other map[string]any) (api.Meter, error) {
 	factory, err := Registry.Get(strings.ToLower(typ))
@@ -19,10 +26,53 @@ func NewFromConfig(ctx context.Context, typ string, other map[string]any) (api.M
 		return nil, err
 	}
 
+	// templates are re-entered with the rendered config, hence handled there
+	var efficiency float64
+	if !strings.EqualFold(typ, "template") {
+		if efficiency, other, err = extractEfficiency(other); err != nil {
+			return nil, fmt.Errorf("cannot create meter type '%s': %w", typ, err)
+		}
+	}
+
 	v, err := factory(ctx, other)
 	if err != nil {
 		return nil, fmt.Errorf("cannot create meter type '%s': %w", util.TypeWithTemplateName(typ, other), err)
 	}
 
+	if efficiency > 0 {
+		caps, ok := v.(implement.Caps)
+		if !ok {
+			return nil, fmt.Errorf("cannot create meter type '%s': %s not supported", typ, efficiencyParam)
+		}
+		implement.Has(caps, implement.BatteryEfficiency(func() float64 { return efficiency }))
+	}
+
 	return v, nil
 }
+
+// extractEfficiency removes the efficiency setting from the config and returns its
+// value in %. It returns 0 if the setting is not configured.
+func extractEfficiency(other map[string]any) (float64, map[string]any, error) {
+	val, ok := other[efficiencyParam]
+	if !ok {
+		return 0, other, nil
+	}
+
+	res := maps.Clone(other)
+	delete(res, efficiencyParam)
+
+	if val == nil || val == "" {
+		return 0, res, nil
+	}
+
+	efficiency, err := cast.ToFloat64E(val)
+	if err != nil {
+		return 0, nil, fmt.Errorf("%s: %w", efficiencyParam, err)
+	}
+
+	if efficiency <= 0 || efficiency > 100 {
+		return 0, nil, fmt.Errorf("%s: invalid value %v", efficiencyParam, val)
+	}
+
+	return efficiency, res, nil
+}
diff --git a/meter/config/config_test.go b/meter/config/config_test.go
new file mode 100644
index 00000000000..aaa23d3a0e6
--- /dev/null
+++ b/meter/config/config_test.go
@@ -0,0 +1,60 @@
+package config
+
+import (
+	"context"
+	"testing"
+
+	"github.com/evcc-io/evcc/api"
+	"github.com/evcc-io/evcc/api/implement"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type testMeter struct {
+	implement.Caps
+}
+
+func (m *testMeter) CurrentPower() (float64, error) {
+	return 0, nil
+}
+
+func TestEfficiency(t *testing.T) {
+	var received map[string]any
+
+	Registry.Add("test-efficiency", func(other map[string]any) (api.Meter, error) {
+		received = other
+		return &testMeter{Caps: implement.New()}, nil
+	})
+
+	for _, tc := range []struct {
+		val      any
+		expected float64
+	}{
+		{nil, 0},
+		{"", 0},
+		{95, 95},
+		{"95", 95},
+		{95.5, 95.5},
+	} {
+		m, err := NewFromConfig(context.TODO(), "test-efficiency", map[string]any{"efficiency": tc.val, "foo": "bar"})
+		require.NoError(t, err, tc)
+
+		// efficiency is not passed on to the device
+		assert.NotContains(t, received, "efficiency", tc)
+		assert.Contains(t, received, "foo", tc)
+
+		eff, ok := api.Cap[api.BatteryEfficiency](m)
+		if tc.expected == 0 {
+			assert.False(t, ok, tc)
+			continue
+		}
+
+		require.True(t, ok, tc)
+		assert.Equal(t, tc.expected, eff.GetEfficiency(), tc)
+	}
+
+	for _, val := range []any{0, -1, 101, "foo"} {
+		_, err := NewFromConfig(context.TODO(), "test-efficiency", map[string]any{"efficiency": val})
+		assert.Error(t, err, val)
+	}
+}
diff --git a/meter/template_test.go b/meter/template_test.go
index 227ca0f063c..7f768dde1f7 100644
--- a/meter/template_test.go
+++ b/meter/template_test.go
@@ -6,6 +6,8 @@ import (
 	"github.com/evcc-io/evcc/api"
 	"github.com/evcc-io/evcc/util/templates"
 	"github.com/evcc-io/evcc/util/test"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 var acceptable = []string{
@@ -48,3 +50,19 @@ func TestTemplates(t *testing.T) {
 		}
 	})
 }
+
+// TestTemplateEfficiency ensures the efficiency setting survives template rendering
+func TestTemplateEfficiency(t *testing.T) {
+	m, err := NewFromConfig(t.Context(), "template", map[string]any{
+		"template":   "demo-battery",
+		"usage":      "battery",
+		"power":      1000,
+		"soc":        50,
+		"efficiency": 95,
+	})
+	require.NoError(t, err)
+
+	eff, ok := api.Cap[api.BatteryEfficiency](m)
+	require.True(t, ok)
+	assert.Equal(t, 95.0, eff.GetEfficiency())
+}
diff --git a/util/templates/defaults.yaml b/util/templates/defaults.yaml
index 13971430a35..7843d2462bf 100644
--- a/util/templates/defaults.yaml
+++ b/util/templates/defaults.yaml
@@ -160,6 +160,18 @@ params:
     example: 95
     type: int
     usages: ["battery"]
+  - name: efficiency
+    unit: "%"
+    description:
+      de: Wirkungsgrad
+      en: Efficiency
+    help:
+      de: Lade- und Entladewirkungsgrad der Batterie für die Optimierung
+      en: Charge and discharge efficiency of the battery used for optimization
+    default: 90
+    advanced: true
+    type: int
+    usages: ["battery"]
   - name: mincurrent
     unit: A
     description:
@@ -823,6 +835,7 @@ presets:
     - name: maxsoc
     - name: maxchargepower
     - name: maxdischargepower
+    - name: efficiency
 
   battery-capacity:
     - name: capacity
diff --git a/util/templates/includes/battery-params.tpl b/util/templates/includes/battery-params.tpl
index 4467af10e0e..3d63f0bb5ef 100644
--- a/util/templates/includes/battery-params.tpl
+++ b/util/templates/includes/battery-params.tpl
@@ -12,8 +12,13 @@ maxchargepower: {{ .maxchargepower }} # W
 maxdischargepower: {{ .maxdischargepower }} # W
 {{- end }}
 
+{{ define "battery-efficiency" }}
+efficiency: {{ .efficiency }} # %
+{{- end }}
+
 {{ define "battery-params" }}
 {{- include "battery-capacity" . }}
 {{- include "battery-minmaxsoc" . }}
 {{- include "battery-power" . }}
+{{- include "battery-efficiency" . }}
 {{- end }}

From 14c07d7c89207f89946ec487498c7277d0797d67 Mon Sep 17 00:00:00 2001
From: andig <cpuidle@gmail.com>
Date: Wed, 22 Jul 2026 11:37:27 +0200
Subject: [PATCH 2/4] Use integer percent efficiency

---
 api/api.go                       | 2 +-
 api/implement/implementations.go | 6 +++---
 core/site_optimizer.go           | 4 +++-
 core/site_optimizer_test.go      | 2 +-
 meter/config/config.go           | 8 ++++----
 meter/config/config_test.go      | 5 ++---
 meter/template_test.go           | 2 +-
 7 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/api/api.go b/api/api.go
index 282e511dc5f..72e21151c44 100644
--- a/api/api.go
+++ b/api/api.go
@@ -61,7 +61,7 @@ type BatterySocLimiter interface {
 
 // BatteryEfficiency provides the battery charge/discharge efficiency in %
 type BatteryEfficiency interface {
-	GetEfficiency() float64
+	Efficiency() int64
 }
 
 // MaxACPowerGetter provides max AC power in W
diff --git a/api/implement/implementations.go b/api/implement/implementations.go
index 01fe1ff4d06..f4dcd0e9ae3 100644
--- a/api/implement/implementations.go
+++ b/api/implement/implementations.go
@@ -53,7 +53,7 @@ func (i *iBatteryController) SetBatteryMode(p0 api.BatteryMode) error {
 	return i.batteryController0(p0)
 }
 
-func BatteryEfficiency(batteryEfficiency0 func() float64) api.BatteryEfficiency {
+func BatteryEfficiency(batteryEfficiency0 func() int64) api.BatteryEfficiency {
 	if batteryEfficiency0 == nil {
 		return nil
 	}
@@ -61,10 +61,10 @@ func BatteryEfficiency(batteryEfficiency0 func() float64) api.BatteryEfficiency
 }
 
 type iBatteryEfficiency struct {
-	batteryEfficiency0 func() float64
+	batteryEfficiency0 func() int64
 }
 
-func (i *iBatteryEfficiency) GetEfficiency() float64 {
+func (i *iBatteryEfficiency) Efficiency() int64 {
 	return i.batteryEfficiency0()
 }
 
diff --git a/core/site_optimizer.go b/core/site_optimizer.go
index 75d5e0e832e..16a40560aed 100644
--- a/core/site_optimizer.go
+++ b/core/site_optimizer.go
@@ -674,7 +674,9 @@ func (site *Site) batteryEta(battery []types.Measurement) float32 {
 
 		e := float64(eta)
 		if m, ok := api.Cap[api.BatteryEfficiency](dev.Instance()); ok {
-			e = m.GetEfficiency() / 100
+			if v := m.Efficiency(); v > 0 {
+				e = float64(v) / 100
+			}
 		}
 
 		sum += e * c
diff --git a/core/site_optimizer_test.go b/core/site_optimizer_test.go
index e9df9b41c4b..4d2bc37fe68 100644
--- a/core/site_optimizer_test.go
+++ b/core/site_optimizer_test.go
@@ -327,7 +327,7 @@ type effMeter struct {
 	api.Meter
 }
 
-func (m effMeter) GetEfficiency() float64 {
+func (m effMeter) Efficiency() int64 {
 	return 100
 }
 
diff --git a/meter/config/config.go b/meter/config/config.go
index 45c885299b4..b5cb0102a12 100644
--- a/meter/config/config.go
+++ b/meter/config/config.go
@@ -27,7 +27,7 @@ func NewFromConfig(ctx context.Context, typ string, other map[string]any) (api.M
 	}
 
 	// templates are re-entered with the rendered config, hence handled there
-	var efficiency float64
+	var efficiency int64
 	if !strings.EqualFold(typ, "template") {
 		if efficiency, other, err = extractEfficiency(other); err != nil {
 			return nil, fmt.Errorf("cannot create meter type '%s': %w", typ, err)
@@ -44,7 +44,7 @@ func NewFromConfig(ctx context.Context, typ string, other map[string]any) (api.M
 		if !ok {
 			return nil, fmt.Errorf("cannot create meter type '%s': %s not supported", typ, efficiencyParam)
 		}
-		implement.Has(caps, implement.BatteryEfficiency(func() float64 { return efficiency }))
+		implement.Has(caps, implement.BatteryEfficiency(func() int64 { return efficiency }))
 	}
 
 	return v, nil
@@ -52,7 +52,7 @@ func NewFromConfig(ctx context.Context, typ string, other map[string]any) (api.M
 
 // extractEfficiency removes the efficiency setting from the config and returns its
 // value in %. It returns 0 if the setting is not configured.
-func extractEfficiency(other map[string]any) (float64, map[string]any, error) {
+func extractEfficiency(other map[string]any) (int64, map[string]any, error) {
 	val, ok := other[efficiencyParam]
 	if !ok {
 		return 0, other, nil
@@ -65,7 +65,7 @@ func extractEfficiency(other map[string]any) (float64, map[string]any, error) {
 		return 0, res, nil
 	}
 
-	efficiency, err := cast.ToFloat64E(val)
+	efficiency, err := cast.ToInt64E(val)
 	if err != nil {
 		return 0, nil, fmt.Errorf("%s: %w", efficiencyParam, err)
 	}
diff --git a/meter/config/config_test.go b/meter/config/config_test.go
index aaa23d3a0e6..8071cd9985c 100644
--- a/meter/config/config_test.go
+++ b/meter/config/config_test.go
@@ -28,13 +28,12 @@ func TestEfficiency(t *testing.T) {
 
 	for _, tc := range []struct {
 		val      any
-		expected float64
+		expected int64
 	}{
 		{nil, 0},
 		{"", 0},
 		{95, 95},
 		{"95", 95},
-		{95.5, 95.5},
 	} {
 		m, err := NewFromConfig(context.TODO(), "test-efficiency", map[string]any{"efficiency": tc.val, "foo": "bar"})
 		require.NoError(t, err, tc)
@@ -50,7 +49,7 @@ func TestEfficiency(t *testing.T) {
 		}
 
 		require.True(t, ok, tc)
-		assert.Equal(t, tc.expected, eff.GetEfficiency(), tc)
+		assert.Equal(t, tc.expected, eff.Efficiency(), tc)
 	}
 
 	for _, val := range []any{0, -1, 101, "foo"} {
diff --git a/meter/template_test.go b/meter/template_test.go
index 7f768dde1f7..3515907e4e7 100644
--- a/meter/template_test.go
+++ b/meter/template_test.go
@@ -64,5 +64,5 @@ func TestTemplateEfficiency(t *testing.T) {
 
 	eff, ok := api.Cap[api.BatteryEfficiency](m)
 	require.True(t, ok)
-	assert.Equal(t, 95.0, eff.GetEfficiency())
+	assert.Equal(t, int64(95), eff.Efficiency())
 }

From 7e50029b4e3eb91e360a180e73026f5f1620dbed Mon Sep 17 00:00:00 2001
From: andig <cpuidle@gmail.com>
Date: Wed, 22 Jul 2026 11:47:38 +0200
Subject: [PATCH 3/4] Use per-battery efficiency

---
 core/site_optimizer.go      | 44 +++++++++----------------------------
 core/site_optimizer_test.go | 29 ++++++++++--------------
 go.mod                      |  2 +-
 go.sum                      |  4 ++--
 4 files changed, 25 insertions(+), 54 deletions(-)

diff --git a/core/site_optimizer.go b/core/site_optimizer.go
index 16a40560aed..684f3b3e4ee 100644
--- a/core/site_optimizer.go
+++ b/core/site_optimizer.go
@@ -320,15 +320,13 @@ func (site *Site) optimizerUpdate(battery []types.Measurement) error {
 		ft = prorate(ftSlots, firstSlotDuration)
 	}
 
-	batteryEta := site.batteryEta(battery)
-
 	req := optimizer.OptimizationInput{
 		Strategy: optimizer.OptimizerStrategy{
 			ChargingStrategy:    optimizer.OptimizerStrategyChargingStrategy(site.GetOptimizerChargingStrategy()),
 			DischargingStrategy: optimizer.OptimizerStrategyDischargingStrategyDischargeBeforeImport,
 		},
-		EtaC: batteryEta,
-		EtaD: batteryEta,
+		EtaC: eta,
+		EtaD: eta,
 		TimeSeries: optimizer.TimeSeries{
 			Dt: dt,
 			Gt: prorate(gt, firstSlotDuration),
@@ -339,7 +337,7 @@ func (site *Site) optimizerUpdate(battery []types.Measurement) error {
 	}
 
 	// end of horizon Wh value
-	pa := lo.Min(req.TimeSeries.PN) * batteryEta * 0.99
+	pa := lo.Min(req.TimeSeries.PN) * eta * 0.99
 
 	details := requestDetails{
 		Timestamps: asTimestamps(dt, now),
@@ -661,35 +659,6 @@ func (site *Site) loadpointRequest(lp loadpoint.API, minLen int, firstSlotDurati
 	return bat, detail
 }
 
-// batteryEta returns the capacity-weighted charge/discharge efficiency of the home
-// batteries. Weighted since the optimizer api only accepts a single global value.
-func (site *Site) batteryEta(battery []types.Measurement) float32 {
-	var sum, capacity float64
-
-	for i, dev := range site.batteryMeters {
-		if i >= len(battery) || battery[i].Capacity == nil {
-			continue
-		}
-		c := *battery[i].Capacity
-
-		e := float64(eta)
-		if m, ok := api.Cap[api.BatteryEfficiency](dev.Instance()); ok {
-			if v := m.Efficiency(); v > 0 {
-				e = float64(v) / 100
-			}
-		}
-
-		sum += e * c
-		capacity += c
-	}
-
-	if capacity == 0 {
-		return eta
-	}
-
-	return float32(sum / capacity)
-}
-
 func (site *Site) batteryRequest(dev config.Device[api.Meter], b types.Measurement, grid api.Rates, minLen int, firstSlotDuration time.Duration) (optimizer.BatteryConfig, batteryDetail) {
 	bat := optimizer.BatteryConfig{
 		CMax:      batteryPower,
@@ -712,6 +681,13 @@ func (site *Site) batteryRequest(dev config.Device[api.Meter], b types.Measureme
 		bat.DMax = float32(discharge)
 	}
 
+	if m, ok := api.Cap[api.BatteryEfficiency](instance); ok {
+		if e := m.Efficiency(); e > 0 {
+			bat.EtaC = float32(e) / 100
+			bat.EtaD = bat.EtaC
+		}
+	}
+
 	if m, ok := api.Cap[api.BatterySocLimiter](instance); ok {
 		minSoc, maxSoc := m.GetSocLimits()
 		if maxSoc == 0 {
diff --git a/core/site_optimizer_test.go b/core/site_optimizer_test.go
index 4d2bc37fe68..5c162c766a6 100644
--- a/core/site_optimizer_test.go
+++ b/core/site_optimizer_test.go
@@ -328,25 +328,20 @@ type effMeter struct {
 }
 
 func (m effMeter) Efficiency() int64 {
-	return 100
+	return 95
 }
 
-func TestBatteryEta(t *testing.T) {
-	device := func(m api.Meter) config.Device[api.Meter] {
-		return config.NewStaticDevice(config.Named{}, m)
-	}
-	measurement := func(capacity float64) types.Measurement {
-		return types.Measurement{Capacity: &capacity}
-	}
-
-	// no batteries
-	assert.Equal(t, eta, (&Site{}).batteryEta(nil))
+func TestBatteryEfficiency(t *testing.T) {
+	site := &Site{}
+	capacity, soc := 10.0, 50.0
+	b := types.Measurement{Capacity: &capacity, Soc: &soc}
 
-	// unconfigured battery uses the default
-	site := &Site{batteryMeters: []config.Device[api.Meter]{device(nil)}}
-	assert.Equal(t, eta, site.batteryEta([]types.Measurement{measurement(10)}))
+	// unconfigured battery leaves the request default
+	bat, _ := site.batteryRequest(config.NewStaticDevice[api.Meter](config.Named{}, nil), b, nil, 1, time.Hour)
+	assert.Zero(t, bat.EtaC)
+	assert.Zero(t, bat.EtaD)
 
-	// capacity-weighted average of 100% (10 kWh) and default 90% (30 kWh)
-	site = &Site{batteryMeters: []config.Device[api.Meter]{device(effMeter{}), device(nil)}}
-	assert.InDelta(t, 0.925, site.batteryEta([]types.Measurement{measurement(10), measurement(30)}), 1e-6)
+	bat, _ = site.batteryRequest(config.NewStaticDevice[api.Meter](config.Named{}, effMeter{}), b, nil, 1, time.Hour)
+	assert.Equal(t, float32(0.95), bat.EtaC)
+	assert.Equal(t, float32(0.95), bat.EtaD)
 }
diff --git a/go.mod b/go.mod
index 6b5112e706f..9b67e3dd428 100644
--- a/go.mod
+++ b/go.mod
@@ -33,7 +33,7 @@ require (
 	github.com/enbility/ship-go v0.6.1-0.20260720110450-0aa90f64ac76
 	github.com/enbility/spine-go v0.7.1-0.20260629113257-b3bcc643f323
 	github.com/evcc-io/openapi-mcp v0.6.1-0.20260701153510-26c442199ef4
-	github.com/evcc-io/optimizer v0.0.0-20260719151136-b6c835a178a3
+	github.com/evcc-io/optimizer v0.0.0-20260722084459-8e6909402d49
 	github.com/evcc-io/rct v0.2.0
 	github.com/evcc-io/tesla-proxy-client v0.0.0-20260722070723-f3604323d820
 	github.com/fatih/structs v1.1.0
diff --git a/go.sum b/go.sum
index 17a4ea78fa4..f0bee6b19ff 100644
--- a/go.sum
+++ b/go.sum
@@ -152,8 +152,8 @@ github.com/evcc-io/ocpp-go v0.0.0-20251212212612-b7f92ee0443b h1:5vFr7wOwoi5ylyb
 github.com/evcc-io/ocpp-go v0.0.0-20251212212612-b7f92ee0443b/go.mod h1:2kcukDdhui4u730VfnYVWuwzDLgw+mBRGDir/QAyBhg=
 github.com/evcc-io/openapi-mcp v0.6.1-0.20260701153510-26c442199ef4 h1:aGM3NwDsKbnmiaO10ptbvEolRAUThWJEsObiAWFDU/c=
 github.com/evcc-io/openapi-mcp v0.6.1-0.20260701153510-26c442199ef4/go.mod h1:YyOx4zwr6xVUcchAETHERZ+75cZMIrdcjVIZFwBlE1Q=
-github.com/evcc-io/optimizer v0.0.0-20260719151136-b6c835a178a3 h1:QXk6AKYrYWQ+PxXhJS/LcHnegKFCCClUQ/BlCuqbs9Y=
-github.com/evcc-io/optimizer v0.0.0-20260719151136-b6c835a178a3/go.mod h1:cHMeq6GfoXQ8LxqY4LH1wn/hrgYEn+ka5RPI1CF37SY=
+github.com/evcc-io/optimizer v0.0.0-20260722084459-8e6909402d49 h1:4rutNWH9/rAdfKEbKIif3u8XuUHR8TnGbZAGffoQR0U=
+github.com/evcc-io/optimizer v0.0.0-20260722084459-8e6909402d49/go.mod h1:cHMeq6GfoXQ8LxqY4LH1wn/hrgYEn+ka5RPI1CF37SY=
 github.com/evcc-io/rct v0.2.0 h1:qjXKI7NKwW5YpEKEb27MwLMBaR4ne2Kd2cPV2PYTKn4=
 github.com/evcc-io/rct v0.2.0/go.mod h1:n6MTBU36QOadGlxxiADu86VaT5l0eYdbmFBHF14AD/s=
 github.com/evcc-io/tesla-proxy-client v0.0.0-20260722070723-f3604323d820 h1:qpLoOYEJ6dgD+UBEgwzsIiQ3WLPmi3Xb7EN4wFIypQY=

From a968a6535a0573f228d3f26a06406365acac1f21 Mon Sep 17 00:00:00 2001
From: andig <cpuidle@gmail.com>
Date: Wed, 22 Jul 2026 13:10:13 +0200
Subject: [PATCH 4/4] Handle efficiency like other battery params

---
 meter/bosch_bpts5_hybrid.go                   |  6 +-
 meter/config/config.go                        | 50 ----------------
 meter/config/config_test.go                   | 59 -------------------
 meter/e3dc.go                                 |  6 +-
 meter/ecoflow.go                              |  6 +-
 meter/homeassistant.go                        |  2 +
 meter/lgess.go                                |  6 +-
 meter/mbmd.go                                 |  2 +
 meter/meter.go                                |  2 +
 meter/powerwall.go                            |  6 +-
 meter/rct.go                                  |  6 +-
 meter/sma.go                                  |  6 +-
 meter/usage_battery.go                        | 16 +++++
 meter/zendure.go                              |  2 +
 .../definition/meter/tesla-powerwall.yaml     |  2 +
 15 files changed, 54 insertions(+), 123 deletions(-)
 delete mode 100644 meter/config/config_test.go

diff --git a/meter/bosch_bpts5_hybrid.go b/meter/bosch_bpts5_hybrid.go
index 1984ec4c179..3c2c2c5a720 100644
--- a/meter/bosch_bpts5_hybrid.go
+++ b/meter/bosch_bpts5_hybrid.go
@@ -25,6 +25,7 @@ func init() {
 func NewBoschBpts5HybridFromConfig(other map[string]any) (api.Meter, error) {
 	var cc struct {
 		batteryCapacity    `mapstructure:",squash"`
+		batteryEfficiency  `mapstructure:",squash"`
 		batteryPowerLimits `mapstructure:",squash"`
 		batterySocLimits   `mapstructure:",squash"`
 		URI                string
@@ -40,11 +41,11 @@ func NewBoschBpts5HybridFromConfig(other map[string]any) (api.Meter, error) {
 		return nil, errors.New("missing usage")
 	}
 
-	return NewBoschBpts5Hybrid(cc.URI, cc.Usage, cc.Cache, cc.batteryCapacity.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
+	return NewBoschBpts5Hybrid(cc.URI, cc.Usage, cc.Cache, cc.batteryCapacity.Decorator(), cc.batteryEfficiency.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
 }
 
 // NewBoschBpts5Hybrid creates a Bosch BPT-S 5 Hybrid Meter
-func NewBoschBpts5Hybrid(uri, usage string, cache time.Duration, capacity func() float64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (*BoschBpts5Hybrid, error) {
+func NewBoschBpts5Hybrid(uri, usage string, cache time.Duration, capacity func() float64, efficiency func() int64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (*BoschBpts5Hybrid, error) {
 	log := util.NewLogger("bosch-bpt")
 
 	instance, exists := bosch.Instances.LoadOrStore(uri, bosch.NewLocal(log, uri, cache))
@@ -65,6 +66,7 @@ func NewBoschBpts5Hybrid(uri, usage string, cache time.Duration, capacity func()
 		implement.May(m, implement.BatteryCapacity(capacity))
 		implement.May(m, implement.BatterySocLimiter(batterySocLimits))
 		implement.May(m, implement.BatteryPowerLimiter(batteryPowerLimits))
+		implement.May(m, implement.BatteryEfficiency(efficiency))
 	}
 
 	return m, nil
diff --git a/meter/config/config.go b/meter/config/config.go
index b5cb0102a12..d516142350a 100644
--- a/meter/config/config.go
+++ b/meter/config/config.go
@@ -3,22 +3,15 @@ package config
 import (
 	"context"
 	"fmt"
-	"maps"
 	"strings"
 
 	"github.com/evcc-io/evcc/api"
-	"github.com/evcc-io/evcc/api/implement"
 	"github.com/evcc-io/evcc/util"
 	reg "github.com/evcc-io/evcc/util/registry"
-	"github.com/spf13/cast"
 )
 
 var Registry = reg.New[api.Meter]("meter")
 
-// efficiencyParam is the battery efficiency setting. It is handled here instead of
-// in the device implementations since it is not used by the device itself.
-const efficiencyParam = "efficiency"
-
 // NewFromConfig creates meter from configuration
 func NewFromConfig(ctx context.Context, typ string, other map[string]any) (api.Meter, error) {
 	factory, err := Registry.Get(strings.ToLower(typ))
@@ -26,53 +19,10 @@ func NewFromConfig(ctx context.Context, typ string, other map[string]any) (api.M
 		return nil, err
 	}
 
-	// templates are re-entered with the rendered config, hence handled there
-	var efficiency int64
-	if !strings.EqualFold(typ, "template") {
-		if efficiency, other, err = extractEfficiency(other); err != nil {
-			return nil, fmt.Errorf("cannot create meter type '%s': %w", typ, err)
-		}
-	}
-
 	v, err := factory(ctx, other)
 	if err != nil {
 		return nil, fmt.Errorf("cannot create meter type '%s': %w", util.TypeWithTemplateName(typ, other), err)
 	}
 
-	if efficiency > 0 {
-		caps, ok := v.(implement.Caps)
-		if !ok {
-			return nil, fmt.Errorf("cannot create meter type '%s': %s not supported", typ, efficiencyParam)
-		}
-		implement.Has(caps, implement.BatteryEfficiency(func() int64 { return efficiency }))
-	}
-
 	return v, nil
 }
-
-// extractEfficiency removes the efficiency setting from the config and returns its
-// value in %. It returns 0 if the setting is not configured.
-func extractEfficiency(other map[string]any) (int64, map[string]any, error) {
-	val, ok := other[efficiencyParam]
-	if !ok {
-		return 0, other, nil
-	}
-
-	res := maps.Clone(other)
-	delete(res, efficiencyParam)
-
-	if val == nil || val == "" {
-		return 0, res, nil
-	}
-
-	efficiency, err := cast.ToInt64E(val)
-	if err != nil {
-		return 0, nil, fmt.Errorf("%s: %w", efficiencyParam, err)
-	}
-
-	if efficiency <= 0 || efficiency > 100 {
-		return 0, nil, fmt.Errorf("%s: invalid value %v", efficiencyParam, val)
-	}
-
-	return efficiency, res, nil
-}
diff --git a/meter/config/config_test.go b/meter/config/config_test.go
deleted file mode 100644
index 8071cd9985c..00000000000
--- a/meter/config/config_test.go
+++ /dev/null
@@ -1,59 +0,0 @@
-package config
-
-import (
-	"context"
-	"testing"
-
-	"github.com/evcc-io/evcc/api"
-	"github.com/evcc-io/evcc/api/implement"
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-)
-
-type testMeter struct {
-	implement.Caps
-}
-
-func (m *testMeter) CurrentPower() (float64, error) {
-	return 0, nil
-}
-
-func TestEfficiency(t *testing.T) {
-	var received map[string]any
-
-	Registry.Add("test-efficiency", func(other map[string]any) (api.Meter, error) {
-		received = other
-		return &testMeter{Caps: implement.New()}, nil
-	})
-
-	for _, tc := range []struct {
-		val      any
-		expected int64
-	}{
-		{nil, 0},
-		{"", 0},
-		{95, 95},
-		{"95", 95},
-	} {
-		m, err := NewFromConfig(context.TODO(), "test-efficiency", map[string]any{"efficiency": tc.val, "foo": "bar"})
-		require.NoError(t, err, tc)
-
-		// efficiency is not passed on to the device
-		assert.NotContains(t, received, "efficiency", tc)
-		assert.Contains(t, received, "foo", tc)
-
-		eff, ok := api.Cap[api.BatteryEfficiency](m)
-		if tc.expected == 0 {
-			assert.False(t, ok, tc)
-			continue
-		}
-
-		require.True(t, ok, tc)
-		assert.Equal(t, tc.expected, eff.Efficiency(), tc)
-	}
-
-	for _, val := range []any{0, -1, 101, "foo"} {
-		_, err := NewFromConfig(context.TODO(), "test-efficiency", map[string]any{"efficiency": val})
-		assert.Error(t, err, val)
-	}
-}
diff --git a/meter/e3dc.go b/meter/e3dc.go
index a9eab925e1f..8218d9781c5 100644
--- a/meter/e3dc.go
+++ b/meter/e3dc.go
@@ -34,6 +34,7 @@ func init() {
 func NewE3dcFromConfig(other map[string]any) (api.Meter, error) {
 	cc := struct {
 		batteryCapacity    `mapstructure:",squash"`
+		batteryEfficiency  `mapstructure:",squash"`
 		batteryPowerLimits `mapstructure:",squash"`
 		batterySocLimits   `mapstructure:",squash"`
 		pvMaxACPower       `mapstructure:",squash"`
@@ -71,12 +72,12 @@ func NewE3dcFromConfig(other map[string]any) (api.Meter, error) {
 		ReceiveTimeout:    cc.Timeout,
 	}
 
-	return NewE3dc(cfg, cc.Usage, cc.DischargeLimit, cc.ExternalPower, cc.batteryCapacity.Decorator(), cc.pvMaxACPower.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
+	return NewE3dc(cfg, cc.Usage, cc.DischargeLimit, cc.ExternalPower, cc.batteryCapacity.Decorator(), cc.pvMaxACPower.Decorator(), cc.batteryEfficiency.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
 }
 
 var e3dcOnce sync.Once
 
-func NewE3dc(cfg rscp.ClientConfig, usage templates.Usage, dischargeLimit uint32, externalPower bool, capacity, maxacpower func() float64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (api.Meter, error) {
+func NewE3dc(cfg rscp.ClientConfig, usage templates.Usage, dischargeLimit uint32, externalPower bool, capacity, maxacpower func() float64, efficiency func() int64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (api.Meter, error) {
 	e3dcOnce.Do(func() {
 		log := util.NewLogger("e3dc")
 		rscp.Log.SetLevel(logrus.DebugLevel)
@@ -108,6 +109,7 @@ func NewE3dc(cfg rscp.ClientConfig, usage templates.Usage, dischargeLimit uint32
 
 	if usage == templates.UsageBattery {
 		implement.May(m, implement.BatteryCapacity(capacity))
+		implement.May(m, implement.BatteryEfficiency(efficiency))
 		implement.Has(m, implement.Battery(m.batterySoc))
 		implement.Has(m, implement.BatteryController(m.setBatteryMode))
 	}
diff --git a/meter/ecoflow.go b/meter/ecoflow.go
index 6109dbfc904..ff19fca4f54 100644
--- a/meter/ecoflow.go
+++ b/meter/ecoflow.go
@@ -34,6 +34,7 @@ func init() {
 func NewEcoFlowFromConfig(other map[string]any) (api.Meter, error) {
 	cc := struct {
 		batteryCapacity                      `mapstructure:",squash"`
+		batteryEfficiency                    `mapstructure:",squash"`
 		batteryPowerLimits                   `mapstructure:",squash"`
 		batterySocLimits                     `mapstructure:",squash"`
 		Usage                                string
@@ -72,12 +73,12 @@ func NewEcoFlowFromConfig(other map[string]any) (api.Meter, error) {
 		return nil, fmt.Errorf("invalid region: %s", cc.Region)
 	}
 
-	return NewEcoFlow(cc.AccessKey, cc.SecretKey, cc.Serial, cc.Usage, uri, cc.Power, cc.Soc, cc.Cache, cc.batteryCapacity.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
+	return NewEcoFlow(cc.AccessKey, cc.SecretKey, cc.Serial, cc.Usage, uri, cc.Power, cc.Soc, cc.Cache, cc.batteryCapacity.Decorator(), cc.batteryEfficiency.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
 }
 
 // NewEcoFlow constructs the EcoFlow struct
 func NewEcoFlow(accessKey, secretKey, serial, usage, uri string,
-	power, soc string, cache time.Duration, capacity func() float64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (*EcoFlow, error) {
+	power, soc string, cache time.Duration, capacity func() float64, efficiency func() int64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (*EcoFlow, error) {
 	log := util.NewLogger("ecoflow").Redact(accessKey, secretKey, serial)
 
 	m := &EcoFlow{
@@ -100,6 +101,7 @@ func NewEcoFlow(accessKey, secretKey, serial, usage, uri string,
 		implement.May(m, implement.BatteryCapacity(capacity))
 		implement.May(m, implement.BatterySocLimiter(batterySocLimits))
 		implement.May(m, implement.BatteryPowerLimiter(batteryPowerLimits))
+		implement.May(m, implement.BatteryEfficiency(efficiency))
 	}
 
 	return m, nil
diff --git a/meter/homeassistant.go b/meter/homeassistant.go
index 22e0233eb42..d9c82924d8a 100644
--- a/meter/homeassistant.go
+++ b/meter/homeassistant.go
@@ -32,6 +32,7 @@ func NewHomeAssistantFromConfig(other map[string]any) (api.Meter, error) {
 
 		// battery
 		batteryCapacity    `mapstructure:",squash"`
+		batteryEfficiency  `mapstructure:",squash"`
 		batterySocLimits   `mapstructure:",squash"`
 		batteryPowerLimits `mapstructure:",squash"`
 
@@ -85,6 +86,7 @@ func NewHomeAssistantFromConfig(other map[string]any) (api.Meter, error) {
 		implement.May(m, implement.BatteryCapacity(cc.batteryCapacity.Decorator()))
 		implement.May(m, implement.BatterySocLimiter(cc.batterySocLimits.Decorator()))
 		implement.May(m, implement.BatteryPowerLimiter(cc.batteryPowerLimits.Decorator()))
+		implement.May(m, implement.BatteryEfficiency(cc.batteryEfficiency.Decorator()))
 
 		if cc.ModeHold != "" || cc.ModeCharge != "" {
 			if cc.ModeNormal == "" {
diff --git a/meter/lgess.go b/meter/lgess.go
index 2052530f904..17735487b52 100644
--- a/meter/lgess.go
+++ b/meter/lgess.go
@@ -36,6 +36,7 @@ func NewLgEss15FromConfig(other map[string]any) (api.Meter, error) {
 func NewLgEssFromConfig(other map[string]any, essType lgpcs.Model) (api.Meter, error) {
 	cc := struct {
 		batteryCapacity        `mapstructure:",squash"`
+		batteryEfficiency      `mapstructure:",squash"`
 		batterySocLimits       `mapstructure:",squash"`
 		batteryPowerLimits     `mapstructure:",squash"`
 		URI, Usage             string
@@ -57,11 +58,11 @@ func NewLgEssFromConfig(other map[string]any, essType lgpcs.Model) (api.Meter, e
 		return nil, errors.New("missing usage")
 	}
 
-	return NewLgEss(cc.URI, cc.Usage, cc.Registration, cc.Password, cc.Cache, cc.batteryCapacity, cc.batterySocLimits, cc.batteryPowerLimits, essType)
+	return NewLgEss(cc.URI, cc.Usage, cc.Registration, cc.Password, cc.Cache, cc.batteryCapacity, cc.batteryEfficiency, cc.batterySocLimits, cc.batteryPowerLimits, essType)
 }
 
 // NewLgEss creates an LgEss Meter
-func NewLgEss(uri, usage, registration, password string, cache time.Duration, batteryCapacity batteryCapacity, batterySocLimits batterySocLimits, batteryPowerLimits batteryPowerLimits, essType lgpcs.Model) (api.Meter, error) {
+func NewLgEss(uri, usage, registration, password string, cache time.Duration, batteryCapacity batteryCapacity, batteryEfficiency batteryEfficiency, batterySocLimits batterySocLimits, batteryPowerLimits batteryPowerLimits, essType lgpcs.Model) (api.Meter, error) {
 	conn, err := lgpcs.GetInstance(uri, registration, password, cache, essType)
 	if err != nil {
 		return nil, err
@@ -83,6 +84,7 @@ func NewLgEss(uri, usage, registration, password string, cache time.Duration, ba
 	if usage == "battery" {
 		implement.Has(m, implement.Battery(m.batterySoc))
 		implement.May(m, implement.BatterySocLimiter(batterySocLimits.Decorator()))
+		implement.May(m, implement.BatteryEfficiency(batteryEfficiency.Decorator()))
 
 		if version, err := conn.GetFirmwareVersion(); err == nil && version >= 7430 {
 			implement.Has(m, implement.BatteryController(m.batteryMode(batterySocLimits)))
diff --git a/meter/mbmd.go b/meter/mbmd.go
index 98fb16cbb3f..42ddf1d2199 100644
--- a/meter/mbmd.go
+++ b/meter/mbmd.go
@@ -31,6 +31,7 @@ func NewMbmdFromConfig(ctx context.Context, other map[string]any) (api.Meter, er
 	cc := struct {
 		Model              string
 		batteryCapacity    `mapstructure:",squash"`
+		batteryEfficiency  `mapstructure:",squash"`
 		batteryPowerLimits `mapstructure:",squash"`
 		batterySocLimits   `mapstructure:",squash"`
 		modbus.Settings    `mapstructure:",squash"`
@@ -124,6 +125,7 @@ func NewMbmdFromConfig(ctx context.Context, other map[string]any) (api.Meter, er
 		implement.May(m, implement.BatteryCapacity(cc.batteryCapacity.Decorator()))
 		implement.May(m, implement.BatterySocLimiter(cc.batterySocLimits.Decorator()))
 		implement.May(m, implement.BatteryPowerLimiter(cc.batteryPowerLimits.Decorator()))
+		implement.May(m, implement.BatteryEfficiency(cc.batteryEfficiency.Decorator()))
 
 		return m, nil
 	}
diff --git a/meter/meter.go b/meter/meter.go
index 0a21ef4e314..d8b1999fbf2 100644
--- a/meter/meter.go
+++ b/meter/meter.go
@@ -28,6 +28,7 @@ func NewConfigurableFromConfig(ctx context.Context, other map[string]any) (api.M
 
 		// battery
 		batteryCapacityCtx    `mapstructure:",squash"`
+		batteryEfficiency     `mapstructure:",squash"`
 		batterySocLimitsCtx   `mapstructure:",squash"`
 		batteryPowerLimitsCtx `mapstructure:",squash"`
 		Soc                   *plugin.Config // optional
@@ -90,6 +91,7 @@ func NewConfigurableFromConfig(ctx context.Context, other map[string]any) (api.M
 		implement.May(m, implement.BatteryCapacity(capacity))
 		implement.May(m, implement.BatterySocLimiter(socLimiter))
 		implement.May(m, implement.BatteryPowerLimiter(powerLimiter))
+		implement.May(m, implement.BatteryEfficiency(cc.batteryEfficiency.Decorator()))
 
 		switch {
 		case cc.Soc != nil && cc.LimitSoc != nil:
diff --git a/meter/powerwall.go b/meter/powerwall.go
index c84d1e2df41..6db01b8d3e2 100644
--- a/meter/powerwall.go
+++ b/meter/powerwall.go
@@ -40,6 +40,7 @@ func NewPowerWallFromConfig(other map[string]any) (api.Meter, error) {
 		Cache                      time.Duration
 		RefreshToken               string
 		SiteId                     int64
+		batteryEfficiency          `mapstructure:",squash"`
 		batterySocLimits           `mapstructure:",squash"`
 		batteryPowerLimits         `mapstructure:",squash"`
 	}{
@@ -74,11 +75,11 @@ func NewPowerWallFromConfig(other map[string]any) (api.Meter, error) {
 		cc.Usage = "solar"
 	}
 
-	return NewPowerWall(cc.URI, cc.Usage, cc.User, cc.Password, cc.Cache, cc.RefreshToken, cc.SiteId, cc.batterySocLimits, cc.batteryPowerLimits)
+	return NewPowerWall(cc.URI, cc.Usage, cc.User, cc.Password, cc.Cache, cc.RefreshToken, cc.SiteId, cc.batteryEfficiency, cc.batterySocLimits, cc.batteryPowerLimits)
 }
 
 // NewPowerWall creates a Tesla PowerWall Meter
-func NewPowerWall(uri, usage, user, password string, cache time.Duration, refreshToken string, siteId int64, batterySocLimits batterySocLimits, batteryPowerLimits batteryPowerLimits) (api.Meter, error) {
+func NewPowerWall(uri, usage, user, password string, cache time.Duration, refreshToken string, siteId int64, batteryEfficiency batteryEfficiency, batterySocLimits batterySocLimits, batteryPowerLimits batteryPowerLimits) (api.Meter, error) {
 	log := util.NewLogger("powerwall").Redact(user, password, refreshToken)
 
 	httpClient := &http.Client{
@@ -150,6 +151,7 @@ func NewPowerWall(uri, usage, user, password string, cache time.Duration, refres
 		implement.Has(m, implement.Battery(m.batterySoc))
 		implement.May(m, implement.BatterySocLimiter(batterySocLimits.Decorator()))
 		implement.May(m, implement.BatteryPowerLimiter(batteryPowerLimits.Decorator()))
+		implement.May(m, implement.BatteryEfficiency(batteryEfficiency.Decorator()))
 
 		res, err := m.client.GetSystemStatus()
 		if err != nil {
diff --git a/meter/rct.go b/meter/rct.go
index 8a323184fdb..d2910f5855e 100644
--- a/meter/rct.go
+++ b/meter/rct.go
@@ -69,6 +69,7 @@ func init() {
 // NewRCTFromConfig creates an RCT from generic config
 func NewRCTFromConfig(ctx context.Context, other map[string]any) (api.Meter, error) {
 	cc := struct {
+		batteryEfficiency  `mapstructure:",squash"`
 		batterySocLimits   `mapstructure:",squash"`
 		batteryPowerLimits `mapstructure:",squash"`
 		pvMaxACPower       `mapstructure:",squash"`
@@ -97,11 +98,11 @@ func NewRCTFromConfig(ctx context.Context, other map[string]any) (api.Meter, err
 		return nil, errors.New("missing usage")
 	}
 
-	return NewRCT(ctx, cc.Uri, cc.Usage, cc.batterySocLimits, cc.batteryPowerLimits, cc.Cache, cc.ExternalPower, cc.Capacity, cc.Capacity2, cc.pvMaxACPower.Decorator())
+	return NewRCT(ctx, cc.Uri, cc.Usage, cc.batteryEfficiency, cc.batterySocLimits, cc.batteryPowerLimits, cc.Cache, cc.ExternalPower, cc.Capacity, cc.Capacity2, cc.pvMaxACPower.Decorator())
 }
 
 // NewRCT creates an RCT meter
-func NewRCT(ctx context.Context, uri, usage string, batterySocLimits batterySocLimits, batteryPowerLimits batteryPowerLimits, cache time.Duration, externalPower bool, capacity, capacity2 float64, maxACPower func() float64) (api.Meter, error) {
+func NewRCT(ctx context.Context, uri, usage string, batteryEfficiency batteryEfficiency, batterySocLimits batterySocLimits, batteryPowerLimits batteryPowerLimits, cache time.Duration, externalPower bool, capacity, capacity2 float64, maxACPower func() float64) (api.Meter, error) {
 	log := util.NewLogger("rct")
 
 	// re-use connections
@@ -174,6 +175,7 @@ func NewRCT(ctx context.Context, uri, usage string, batterySocLimits batterySocL
 		implement.Has(m, implement.Battery(batterySoc))
 		implement.May(m, implement.BatterySocLimiter(batterySocLimits.Decorator()))
 		implement.May(m, implement.BatteryPowerLimiter(batteryPowerLimits.Decorator()))
+		implement.May(m, implement.BatteryEfficiency(batteryEfficiency.Decorator()))
 
 		if capacity != 0 {
 			implement.Has(m, implement.BatteryCapacity(func() float64 { return capacity + capacity2 }))
diff --git a/meter/sma.go b/meter/sma.go
index 26a9f847b2a..ef78e40d46e 100644
--- a/meter/sma.go
+++ b/meter/sma.go
@@ -32,6 +32,7 @@ func init() {
 func NewSMAFromConfig(other map[string]any) (api.Meter, error) {
 	cc := struct {
 		batteryCapacity          `mapstructure:",squash"`
+		batteryEfficiency        `mapstructure:",squash"`
 		batteryPowerLimits       `mapstructure:",squash"`
 		batterySocLimits         `mapstructure:",squash"`
 		URI, Password, Interface string
@@ -48,11 +49,11 @@ func NewSMAFromConfig(other map[string]any) (api.Meter, error) {
 		return nil, err
 	}
 
-	return NewSMA(cc.URI, cc.Password, cc.Interface, cc.Serial, cc.Scale, cc.Usage, cc.DC, cc.batteryCapacity.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
+	return NewSMA(cc.URI, cc.Password, cc.Interface, cc.Serial, cc.Scale, cc.Usage, cc.DC, cc.batteryCapacity.Decorator(), cc.batteryEfficiency.Decorator(), cc.batterySocLimits.Decorator(), cc.batteryPowerLimits.Decorator())
 }
 
 // NewSMA creates an SMA meter
-func NewSMA(uri, password, iface string, serial uint32, scale float64, usage string, dc bool, capacity func() float64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (*SMA, error) {
+func NewSMA(uri, password, iface string, serial uint32, scale float64, usage string, dc bool, capacity func() float64, efficiency func() int64, batterySocLimits, batteryPowerLimits func() (float64, float64)) (*SMA, error) {
 	sm := &SMA{
 		Caps:  implement.New(),
 		uri:   uri,
@@ -97,6 +98,7 @@ func NewSMA(uri, password, iface string, serial uint32, scale float64, usage str
 		implement.May(sm, implement.BatteryCapacity(capacity))
 		implement.May(sm, implement.BatterySocLimiter(batterySocLimits))
 		implement.May(sm, implement.BatteryPowerLimiter(batteryPowerLimits))
+		implement.May(sm, implement.BatteryEfficiency(efficiency))
 	}
 
 	if isHybridInverter && usage == "pv" {
diff --git a/meter/usage_battery.go b/meter/usage_battery.go
index 213ca642850..038ab24405f 100644
--- a/meter/usage_battery.go
+++ b/meter/usage_battery.go
@@ -82,6 +82,22 @@ func floatOr0(g func() float64) float64 {
 	return g()
 }
 
+type batteryEfficiency struct {
+	Efficiency int64 // %
+}
+
+// var _ api.BatteryEfficiency = (*batteryEfficiency)(nil)
+
+// Decorator returns an api.BatteryEfficiency decorator
+func (m *batteryEfficiency) Decorator() func() int64 {
+	if m.Efficiency <= 0 || m.Efficiency > 100 {
+		return nil
+	}
+	return func() int64 {
+		return m.Efficiency
+	}
+}
+
 type batteryPowerLimits struct {
 	MaxChargePower    float64
 	MaxDischargePower float64
diff --git a/meter/zendure.go b/meter/zendure.go
index 984bd693140..4245b1f62e4 100644
--- a/meter/zendure.go
+++ b/meter/zendure.go
@@ -25,6 +25,7 @@ type Zendure struct {
 func NewZendureFromConfig(other map[string]any) (api.Meter, error) {
 	cc := struct {
 		batteryCapacity                `mapstructure:",squash"`
+		batteryEfficiency              `mapstructure:",squash"`
 		batteryPowerLimits             `mapstructure:",squash"`
 		batterySocLimits               `mapstructure:",squash"`
 		Usage, Account, Serial, Region string
@@ -55,6 +56,7 @@ func NewZendureFromConfig(other map[string]any) (api.Meter, error) {
 		implement.May(m, implement.BatteryCapacity(cc.batteryCapacity.Decorator()))
 		implement.May(m, implement.BatterySocLimiter(cc.batterySocLimits.Decorator()))
 		implement.May(m, implement.BatteryPowerLimiter(cc.batteryPowerLimits.Decorator()))
+		implement.May(m, implement.BatteryEfficiency(cc.batteryEfficiency.Decorator()))
 	}
 
 	return m, nil
diff --git a/templates/definition/meter/tesla-powerwall.yaml b/templates/definition/meter/tesla-powerwall.yaml
index cddf39003c4..639ae545807 100644
--- a/templates/definition/meter/tesla-powerwall.yaml
+++ b/templates/definition/meter/tesla-powerwall.yaml
@@ -42,6 +42,7 @@ params:
     advanced: true
   - name: maxchargepower
   - name: maxdischargepower
+  - name: efficiency
 render: |
   type: powerwall
   uri: {{ .host }}
@@ -54,3 +55,4 @@ render: |
   maxsoc: {{ .maxsoc }}
   maxchargepower: {{ .maxchargepower }}
   maxdischargepower: {{ .maxdischargepower }}
+  efficiency: {{ .efficiency }}