diff --git a/core/site.go b/core/site.go
index 37290e5674b..da95ed7bc2e 100644
--- a/core/site.go
+++ b/core/site.go
@@ -915,14 +915,7 @@ func (site *Site) update(lp updater) {
 
 	batteryGridChargeActive := site.batteryGridChargeActive(rate)
 	site.publish(keys.BatteryGridChargeActive, batteryGridChargeActive)
-
-	if batteryMode := site.requiredBatteryMode(batteryGridChargeActive, rate); batteryMode != api.BatteryUnknown {
-		if err := site.applyBatteryMode(batteryMode); err == nil {
-			site.SetBatteryMode(batteryMode)
-		} else {
-			site.log.ERROR.Println("battery mode:", err)
-		}
-	}
+	site.updateBatteryMode(batteryGridChargeActive, rate)
 
 	if sitePower, batteryBuffered, batteryStart, err := site.sitePower(totalChargePower, flexiblePower); err == nil {
 		// ignore negative pvPower values as that means it is not an energy source but consumption
diff --git a/core/site_api.go b/core/site_api.go
index d10cd92cb18..23c13aeac86 100644
--- a/core/site_api.go
+++ b/core/site_api.go
@@ -364,19 +364,15 @@ func (site *Site) SetBatteryModeExternal(mode api.BatteryMode) {
 		site.batteryModeExternal = mode
 		site.publish(keys.BatteryModeExternal, mode)
 
-		if !disable {
-			site.setBatteryMode(mode)
-
-			// start watchdog if not running
-			if site.batteryModeExternalTimer.IsZero() {
-				go func() {
-					for range time.Tick(time.Second) {
-						if site.batteryModeWatchdogExpired() {
-							return
-						}
+		// start watchdog if not running
+		if !disable && site.batteryModeExternalTimer.IsZero() {
+			go func() {
+				for range time.Tick(time.Second) {
+					if site.batteryModeWatchdogExpired() {
+						return
 					}
-				}()
-			}
+				}
+			}()
 		}
 	}
 
diff --git a/core/site_battery.go b/core/site_battery.go
index f9d09eb7bb8..3ad41120d59 100644
--- a/core/site_battery.go
+++ b/core/site_battery.go
@@ -39,6 +39,16 @@ func (site *Site) SetBatteryMode(batMode api.BatteryMode) {
 	}
 }
 
+func (site *Site) updateBatteryMode(batteryGridChargeActive bool, rate api.Rate) {
+	if batteryMode := site.requiredBatteryMode(batteryGridChargeActive, rate); batteryMode != api.BatteryUnknown {
+		if err := site.applyBatteryMode(batteryMode); err == nil {
+			site.SetBatteryMode(batteryMode)
+		} else {
+			site.log.ERROR.Println("battery mode:", err)
+		}
+	}
+}
+
 // requiredBatteryMode determines required battery mode based on grid charge and rate
 func (site *Site) requiredBatteryMode(batteryGridChargeActive bool, rate api.Rate) api.BatteryMode {
 	var res api.BatteryMode
@@ -63,7 +73,10 @@ func (site *Site) requiredBatteryMode(batteryGridChargeActive bool, rate api.Rat
 		// require normal mode to leave external control
 		res = api.BatteryNormal
 	case extMode != api.BatteryUnknown:
-		res = extMode
+		// require external mode only once
+		if extMode != batMode {
+			res = extMode
+		}
 	case batteryGridChargeActive:
 		res = mapper(api.BatteryCharge)
 	case site.dischargeControlActive(rate):
diff --git a/core/site_battery_test.go b/core/site_battery_test.go
index 16a1528a712..61782b2e5a0 100644
--- a/core/site_battery_test.go
+++ b/core/site_battery_test.go
@@ -8,9 +8,10 @@ import (
 	"github.com/evcc-io/evcc/util"
 	"github.com/evcc-io/evcc/util/config"
 	"github.com/stretchr/testify/assert"
+	"go.uber.org/mock/gomock"
 )
 
-func TestExternalBatteryMode(t *testing.T) {
+func TestRequiredExternalBatteryMode(t *testing.T) {
 	for _, tc := range []struct {
 		internal, ext, new api.BatteryMode
 	}{
@@ -19,12 +20,12 @@ func TestExternalBatteryMode(t *testing.T) {
 		{api.BatteryUnknown, api.BatteryCharge, api.BatteryCharge},
 
 		{api.BatteryNormal, api.BatteryUnknown, api.BatteryUnknown},
-		{api.BatteryNormal, api.BatteryNormal, api.BatteryNormal},
+		{api.BatteryNormal, api.BatteryNormal, api.BatteryUnknown}, // no change required
 		{api.BatteryNormal, api.BatteryCharge, api.BatteryCharge},
 
 		{api.BatteryCharge, api.BatteryUnknown, api.BatteryNormal},
 		{api.BatteryCharge, api.BatteryNormal, api.BatteryNormal},
-		{api.BatteryCharge, api.BatteryCharge, api.BatteryCharge},
+		{api.BatteryCharge, api.BatteryCharge, api.BatteryUnknown}, // no change required
 	} {
 		t.Logf("%+v", tc)
 
@@ -42,8 +43,20 @@ func TestExternalBatteryMode(t *testing.T) {
 }
 
 func TestExternalBatteryModeChange(t *testing.T) {
+	ctrl := gomock.NewController(t)
+
+	var bat api.Meter
+	batCon := api.NewMockBatteryController(ctrl)
+
+	bat = &struct {
+		api.Meter
+		api.BatteryController
+	}{
+		BatteryController: batCon,
+	}
+
 	for _, tc := range []struct {
-		internal, ext, expired api.BatteryMode
+		internal, ext, expected api.BatteryMode
 	}{
 		{api.BatteryUnknown, api.BatteryUnknown, api.BatteryNormal},
 		{api.BatteryUnknown, api.BatteryNormal, api.BatteryNormal},
@@ -61,20 +74,31 @@ func TestExternalBatteryModeChange(t *testing.T) {
 
 		site := &Site{
 			log:           util.NewLogger("foo"),
-			batteryMeters: []config.Device[api.Meter]{nil},
+			batteryMeters: []config.Device[api.Meter]{config.NewStaticDevice(config.Named{}, bat)},
 		}
 
+		// set initial state, internal mode may already be changed
 		site.batteryMode = tc.internal
-
+		site.batteryModeExternal = api.BatteryUnknown
 		assert.True(t, site.batteryModeExternalTimer.IsZero())
+
+		// 1. set required external mode
 		site.SetBatteryModeExternal(tc.ext)
+		assert.Equal(t, site.batteryModeExternal, tc.ext, "external mode expected %s got %s", tc.ext, site.batteryModeExternal)
+		assert.Equal(t, site.batteryMode, tc.internal, "internal mode expected unchanged %s got %s", tc.ext, site.batteryMode)
 
-		// timer started
+		// 2. verify external mode applied to battery
 		if tc.ext != api.BatteryUnknown {
-			assert.False(t, site.batteryModeExternalTimer.IsZero())
+			batCon.EXPECT().SetBatteryMode(tc.ext).Times(1)
 		}
+		site.updateBatteryMode(false, api.Rate{})
+		ctrl.Finish()
 
-		// expire timer
+		// 3. verify required external mode only applied once
+		site.updateBatteryMode(false, api.Rate{})
+		ctrl.Finish()
+
+		// 4. verify timer expiry
 		site.batteryModeExternalTimer = site.batteryModeExternalTimer.Add(-time.Hour)
 		site.batteryModeWatchdogExpired()
 
@@ -82,11 +106,12 @@ func TestExternalBatteryModeChange(t *testing.T) {
 		assert.Equal(t, site.batteryModeExternal, api.BatteryUnknown)
 		assert.False(t, site.batteryModeExternalTimer.IsZero())
 
-		mode := site.requiredBatteryMode(false, api.Rate{})
-		assert.Equal(t, tc.expired.String(), mode.String(), "external mode expected %s got %s", tc.expired, mode)
+		// battery switched back to normal mode
+		batCon.EXPECT().SetBatteryMode(api.BatteryNormal).Times(1)
+		site.updateBatteryMode(false, api.Rate{})
+		ctrl.Finish()
 
 		// timer disabled
-		site.SetBatteryMode(mode)
 		assert.True(t, site.batteryModeExternalTimer.IsZero())
 	}
 }