Battery Banks: Wiring Batteries in Parallel and Series


Using a bank of batteries provides an increase in voltage when they are wired together in a series. Connecting them in parallel boosts both the total current capacity and the overall amp-hour capacity. Doing so means that the needs of those applications that require more amperage, voltage or both can be met by wiring batteries together instead of investing in a larger and heavier battery. 

How to wire up a battery bank

There are two main ways that batteries can be wired: in a series or parallel to each other. While the process to wire them together is basically the same — use jumper wire to connect the appropriate terminals — the procedure differs depending on which method is being used. 

  • Wiring up batteries in series

By wiring batteries in a series, voltage is increased but the overall amp-hour capacity does not. The amp-hour rating on each battery in a series bank must be the same. 

Connecting batteries in a series means placing one right after another. To be effective, the battery terminals must be placed in the correct order. The positive end of one battery needs to be wired to the negative end of the one that is next in the series.

Use jumper wire to connect the terminals of the batteries in the series. Then use a set of cables to connect the open negative and positive terminals to the application. Using batteries with the same capacity rating and voltage keeps any potential charging problems to a minimum and won't impact battery life. 

  • Wiring up batteries in parallel

In contrast to wiring batteries in a series, those in parallel increase both overall amp-hour capacity and total current capacity. This last increase is accomplished by a decrease in total resistance. In a parallel bank, each battery must have an identical voltage rating. 

Because the batteries amperage is increased during a parallel connection, it's likely that a heavy-duty cable will be necessary. Otherwise, the cable might burn out. 

Wire up batteries in parallel by connecting both positive terminals with a jumper wire. Use a different jumper wire to connect both negative terminals to each other. In order to keep the batteries equalized, connect to the positive at one end of the battery bank and the negative at the other. However, it is possible to connect the application to one of the batteries and it will still drain both equally. 

  • Using a combination of series and parallel

It's also possible to wire batteries together in both a parallel and series configuration. By doing so, both the amp/hour rating and voltage output are increased. Four batteries are required in order to wire them together in this manner. 

Wire the batteries up in parallel first before joining them together to form a series. Only a single cable is needed because it acts as the bridge between the positive and negative terminals of two separate parallel banks. This is acceptable if a terminal has more than one cable attached to it.

Theoretically, it's possible to wire together as many batteries as desired — though this could result in a confusing and unsafe situation. To keep track of connections, particularly those that are complex and that involve a number of batteries and cables, make a diagram of the battery banks prior to constructing them. Doing so could increase safety and reduce confusion.