Batteries for Solar
Do you know if the existing (12V) batteries are connected in parallel or series? Series would be, the negative (-) post of one battery will be connected to the positive (+) post of the other battery. Then there will be a connection running from the negative post of one and the positive post of the other to the inverter. I've not had time to check out my set up. For efficiency, solar system battery banks do typically use 6V batteries, but will be connected in series to make a 48V or 24V system that feeds DC power to the inverter, which converts the DC power to AC power to run your TV, Fridge and all other 110V items. If your batteries are connected in series, you will need two more 6V batteries. If they are connected in parallel, you will need to stick with two 12V batteries.