There are two ways to wire 12-volt batteries, either through a series connection or through a parallel connection. The series connection will add up the voltages of the batteries. In other words, if you wire two 12-volt batteries in series the total voltage from that battery bank will equal 24 volts. A parallel connection keeps the voltage constant, but adds up the current of the battery. If you wire up two 12-volt batteries that are capable of delivering 500 amperes each, the final ampere capacity will be 1,000 amperes, but still deliver 12 volts.
Clean the battery terminal posts on the batteries using the steel brush. The end result should be a shiny metallic finish to each lead terminal.
Observe the markings on the battery terminals. There is a negative (-) terminal and a positive (+) terminal.
Attach the battery clamps to the battery terminals. Slide the clamp over the top of the terminal and press down. Use the ½-inch end wrench to tighten the clamp bolts onto the battery terminal.
Use the 7/16-inch end wrench to loosen the cable clamps on the end of the battery clamps.
Make a series connection for the 12-volt batteries by connecting the negative terminal from the first battery to the positive terminal on the second battery with the battery cable. Tighten the cable into the battery cable clamp using the end wrench. Connect the positive terminal from the first battery to the negative terminal on the second battery. The two batteries are now connected in series for a total of 24 volts.
Connect the two batteries in a parallel connection. Secure a single battery cable to the two positive terminals on each of the two batteries. Attach another single cable between the two negative terminals on each of the two batteries. This will make a parallel connection that will add up the current of the two batteries but keep the voltage at 12 volts.