Feature Request: Add sensor/display for current battery reserve (Backup Buffer)

[djto]

Hi,

First, thank you for your work on this integration, it provides excellent insight into my SonnenBatterie’s status!

I’ve noticed that while the integration lets me set the battery reserve, there is no way to view the actual value directly as a sensor in Home Assistant.

Would it be possible to implement a sensor that reports the current battery reserve (backup buffer) or make the battery_reserve number entity reflect the actual reserve value? This would allow users to monitor and automate around the backup capacity without having to manually call the get_battery_reserve service.

Thank you for considering this feature request, and please let me know if any additional information or testing is needed!

Best regards,
Tobias