It wasn't long ago when trailers or motor homes had only a single 12-volt house battery. Today it's standard to recreational vehicle batteries powering inverters .
DEEP CYCLE BATTERY VOLTAGE & STATE OF CHARGE.
table of automotive battery groups and their dimensions.. PASSENGER CAR AND LIGHT COMMERCIAL_BATTERIES 12-VOLT (6 CELLS). 21, 208, 173, 222
State of charge 12 volt Standard Batteries. Battery state of charge is determined by reading either terminal voltage or the specific gravity of the electrolyte.