Victron Energy BMV-712 Smart Battery Monitor (Grey)

From the brand

Victron Energy BMV-712 features an additional input which can be programmed to measure battery temperature (temperature sensor sold separately), midpoint voltage, or voltage of a second battery, plus a relay that can be programmed to control other devices (such as a battery protect or generator)
Built-in Bluetooth Communication – wirelessly monitor your batteries on smartphones, tablets, and other devices. Or, connect to a GX device via VE.Direct cable (sold separately) and monitor anywhere in the world with VRM
Displays % State of Charge, Voltage, Current, Energy/Time remaining, and more. View historical data and charts in Victron Connect. Easy to Program for initial setup on the display or via bluetooth
Incorrect installation can be hazardous, Please consult a licensed professional and follow all applicable electrical codes during installation