How to Convert 12 Volt to 220 Multiple Batteries

Lay your 18 car batteries, each with a rated output of 12 volts, fully charged (check for state of charge with your multimeter) on a flat surface, side by side. Each battery should be oriented so that the negative terminal is next to a positive terminal on the next battery and vice versa.

Wire together your batteries in series. This will require you to connect the negative terminal of one battery to the positive terminal of the battery next to it. Repeat this step, connecting each negative terminal to the positive terminal on the battery next to it. It may work to your advantage to arrange the batteries in a large circle so that you have access to the positive terminal on the first battery, and the negative terminal on the last battery; do not connect these first and last terminals in the string of batteries.

Turn on your multimeter and set it to measure DC voltage. Touch the black negative probe lead from your meter to the negative terminal on the last battery, and the red positive probe lead to the positive terminal on the first battery. The display on your meter should read between 210 and 230 volts if all of the batteries were adequately charged.