How do you wire 3 12 volt batteries in series?

To wire three 12-volt batteries in series, connect the positive terminal of the first battery to the negative terminal of the second battery. Then, connect the positive terminal of the second battery to the negative terminal of the third battery. Finally, the free positive terminal of the third battery and the free negative terminal of the first battery will serve as the output terminals, providing a total of 36 volts (12V + 12V + 12V). Make sure to double-check connections for safety and correct polarity.