Batteries are connected in series to increase their total voltage, in parallel to increase the available AH (Ampere-Hours) while keeping the voltage the same and in series-parallel to increase both the AHS and voltage.
Connecting the negative terminal of the first battery to the positive terminal of the next battery creates the series configuration.
Connecting the negative terminals together and the positive terminals together creates the parallel configuration.
Connecting the negative terminals of the first battery in a series string with the negative terminal of the first battery in the next series string and the positive terminal of the last battery in the first series string with the positive terminal of the last battery in the next series string creates the series-parallel configuration.
Position the batteries, measure the distance between their positive and negative posts and add 6 inches for flexibility. Cut the required number of pieces of battery cable from the bulk cable. Strip 1 inch of insulation from the ends of each piece.
Select one positive and one negative battery clamp for each jump lead. At first glance, these clamps may look alike, but they aren't. The positive battery post has a larger diameter than the negative and requires a larger clamp. Coat the stripped end of the cable with antioxidant grease, seat it fully in the clamp and secure with the compression Allen screw.
Connect the batteries together, positive terminal to negative, leaving the negative terminal of the first battery and the positive terminal of the last battery unconnected. The total voltage available from 12v batteries connected in series depends on the number of batteries in the series string. For example, three 12v batteries produces 36 volts. Caution: Do not connect the first and last batteries together to form a complete circuit. This will be a direct short, and the batteries may explode.
Position the batteries so that all their negative terminals are on one side and all their positive terminals are on the other side. Measure the distance between posts of like polarity, and cut the battery jumpers to length. Remember to add 4 inches to each piece for flexibility. Strip 1 inch of insulation from each end of each jumper.
Select two of the negative clamps for each negative jumper and two positive clamps for each positive jumper. Assemble the clamps to the cable the same as in Step 2 above.
Using the jumpers, connect all the negative terminals together and all the positive terminals together. In this configuration, the output voltage will remain 12V no matter how many batteries are used. The available current in AH, however, will depend on the AH rating of each battery and the total number of batteries. For example, five batteries of 150 AH each would produce 750AH. For best results, all batteries should have the same AH rating.
Wire the series strings as you did in Section 1 of this article.
Connect each series string in parallel by connecting the negative terminals of the first battery in each string together and the positive terminals of the last battery in each string together.
In this configuration, both the voltage and the AH rating is increased. In this configuration, there has to be an equal number of 12v batteries in each series string, and each battery should have the same AH rating.
Auto batteries contain an electrolyte solution that includes sulphuric acid, which can damage your clothing, burn your skin and blind you if it gets in your eyes. Although modern batteries are sealed, they can develop leaks, so always wear rubber gloves and eye protection when working with these batteries. These batteries can also explode if a direct short occurs across them, so use extreme caution when working with them