1 battery or 2

2 batteries depending on wiring will either get you 12 volts and double the amps or 24 volts and the same amps. It won't help on your lack of supply. I recommend the choice of an alternator or if not go with the 16 volt battery, at least you have 2 volts more so it will stay high during the run, just remember you need to keep it charged after each run