diff --git a/templates/definition/meter/solplanet-ai-dongle.yaml b/templates/definition/meter/solplanet-ai-dongle.yaml
index 979dbb046a..b16ccb7b3d 100644
--- a/templates/definition/meter/solplanet-ai-dongle.yaml
+++ b/templates/definition/meter/solplanet-ai-dongle.yaml
@@ -8,9 +8,20 @@ requirements:
     de: |
       Nutzt die lokale HTTP-Schnittstelle des AI-Dongle (z.B. BA121T-30) statt Modbus TCP.
       Die Seriennummer (isn) des Wechselrichters kann über `http://<host>:8484/getdev.cgi?device=2` ausgelesen werden.
+
+      Die Batteriesteuerung (normal/hold/charge) nutzt fest vorberechnete Modbus-RTU-Befehle,
+      die über die ebenfalls undokumentierte `fdbg.cgi`-Schnittstelle gesendet werden
+      ([Hintergrund und weitere Tester in Diskussion #17680](https://github.com/evcc-io/evcc/discussions/17680)).
+      Da die Befehle fest kodiert sind, ist die Ladeleistung auf 5000 W fixiert.
     en: |
       Uses the AI-Dongle local HTTP API (e.g. BA121T-30) instead of Modbus TCP.
       The inverter serial number (isn) can be read via `http://<host>:8484/getdev.cgi?device=2`.
+
+      Battery control (normal/hold/charge) uses fixed, pre-computed Modbus-RTU commands sent
+      through the equally undocumented `fdbg.cgi` endpoint
+      ([background and more testers in discussion #17680](https://github.com/evcc-io/evcc/discussions/17680)).
+      Because the commands are fixed, charge power is pinned to 5000 W.
+capabilities: ["battery-control"]
 params:
   - name: usage
     choice: ["grid", "pv", "battery"]
@@ -44,5 +55,53 @@ render: |
     source: http
     uri: http://{{ .host }}:8484/getdevdata.cgi?device=4&sn={{ .serial }}
     jq: .soc
+  batterymode:
+    source: switch
+    switch:
+      - case: 1 # normal
+        set:
+          source: http
+          uri: http://{{ .host }}:8484/fdbg.cgi
+          method: POST
+          timeout: 20s
+          headers:
+            Content-Type: application/json
+          body: '{"data":"0306044f0002390e"}' # write reg 1103 (mode) = 2 (normal)
+      - case: 2 # hold: custom mode + 0 W
+        set:
+          source: sequence
+          set:
+            - source: http
+              uri: http://{{ .host }}:8484/fdbg.cgi
+              method: POST
+              timeout: 20s
+              headers:
+                Content-Type: application/json
+              body: '{"data":"0306044f0004b90c"}' # write reg 1103 (mode) = 4 (custom)
+            - source: http
+              uri: http://{{ .host }}:8484/fdbg.cgi
+              method: POST
+              timeout: 20s
+              headers:
+                Content-Type: application/json
+              body: '{"data":"03060480000088f0"}' # write reg 1152 (setpoint) = 0 W
+      - case: 3 # charge: custom mode + fixed 5000 W (see requirements)
+        set:
+          source: sequence
+          set:
+            - source: http
+              uri: http://{{ .host }}:8484/fdbg.cgi
+              method: POST
+              timeout: 20s
+              headers:
+                Content-Type: application/json
+              body: '{"data":"0306044f0004b90c"}' # write reg 1103 (mode) = 4 (custom)
+            - source: http
+              uri: http://{{ .host }}:8484/fdbg.cgi
+              method: POST
+              timeout: 20s
+              headers:
+                Content-Type: application/json
+              body: '{"data":"03060480ec78c412"}' # write reg 1152 (setpoint) = -5000 W
   {{- include "battery-params" . }}
-  {{- end }}
+  {{- end }}
\ No newline at end of file