So what you exactly need out of that device? Battery voltage and two pump status (on/off) ?
By what I can tell, and my thoughts…
Primary Pump runs from 110V wall, only power monitoring required
- already done with Sonoff S31
Need to power esp device off 12V battery
Secondary Pump runs from 12V car battery
- Need to charge 12V battery (trickle charge?)
- Need to monitor 12V battery level
- Secondary pump is connected to power by PLA type connectors
- Need to monitor float by PLA type connectors
- This turn on/off power to secondary pump
- Need to alert when running on/off battery or low battery (This can be done either on device (maybe an audible alert? or in HA))
So only the pump and battery are left from original setup and you want full control. While doable, it’s not simple task.
unfortunately, less then a month until this sump pump battery backup becomes dumb, and I don’t have a solution together yet.