12V (12-volt) batteries can be used to power a 24V inverter when the batteries are connected in series, to double their normal output voltage. Save money by using inexpensive 12V batteries instead of buying speciality 24V batteries. Combine two batteries in a series to double the voltage output using a short, heavy-duty cable that is designed to safely connect the positive terminal of one battery to the negative terminal of the other battery.
Clean the battery terminals with a wire brush if they are corroded.
Connect the terminal-to-terminal battery cable to the positive terminal, as indicated by the red colour codings and the "+" symbol, on the first battery, and to the negative terminal, as indicated by the black colour coding and the "-" symbol, on the second battery. Tighten each connection.
Connect the negative "-" terminal lead from the inverter (black) to the negative "-" terminal on the first battery.
Connect the positive "+" terminal lead from the inverter (red) to the positive "+" terminal on the second battery.
Ensure batteries are full of acid or acid and water at all times. Clean the terminals completely before connecting battery cables to terminals. Tighten all connections.
Keep batteries in a well-ventilated area as dangerous fumes are given off over time that can be hazardous to inhale or explosive when ignited. Avoid short circuit situations when the positive lead of a battery or bank of batteries comes in direct contact with the negative lead of the same battery or bank of batteries and forms a complete circuit without any load attached.