I am assuming you have 2 batteries right now, 1 being the starter, 2 being the house battery. I typically when on anchor switch to the house battery which is a deep cycle battery. I can go all weekend long running stereo and lights without a problem Can go 24 hours easy running cabin refrig, stereo, TV and lights. Usually when out for a weekend will start the generator and run for about an hour charging batteries. If I ever added a 3rd battery I would dedicate to the generator. For now just watch the voltage meter in the cabin, when it falls below 12 volts you are getting close to the end. As for the pump to inflate the tender, I am assuming the boat does not have a generator (if so, start and use a pump that plugs in), if not you could add an inverter to create the required power for an AC pump.