battery

My information is based on what I find when checking voltage of two deep cycle 6volt house batteries in series connected to converter/charger with motorhome connected to 110vac shore power or when disconnected from shore power and engine alternator is charging batteries. Yes, there is a "surface charge voltage" of around 13.6 volts which gradually lowers to around 12.6 volts when batteries are not being charged.(if good batteries). Voltage readings may differ depending on battery condition, state of charge, resistance in battery connections, etc. From everything I have read, running lead/acid batteries down to where lights dim is hard on any batteries and to be avoided for longest useful life.