I found out I can automate my 5,12kWh house battery through local-only RS485 connection, and directly setting registers using ModbusTCP from Home Assistant. I then drafted an automation with hysteresis and damping that tries to aim for Net-Zero export/import (pv surplus/grid). It appears to work!
The deranged thing about RS485 and modbus is it's old cheap and just works.
What brand/make of battery is that? I'm tentatively interested in home battery storage, but definitely not interested in shit that requires an app, an internet connection, and shitty saas spyware...