Battery Connection type: Series (Increases Voltage)

Connecting batteries in series means to connect the positive terminal of the first battery to the negative terminal of the second battery and so on down the string.

The interconnecting cables must have equal lengths and resistance to equalize of the load. All batteries in the string will receive the same amount of charge current, though individual battery voltages may vary.

High voltage strings of batteries in series should be limited to twenty 6 volt or ten 12 volt batteries when a single constant voltage charger is connected across the entire string. Differences in capacity can cause some batteries to overcharge while others remain undercharged thus causing premature aging of batteries. It is, therefore, not advisable to mix batteries of different capacities, make, or age in a series string.

For a visual demonstration of this type battery connection, you may refer to the following image, which shows how two units of 12V 65Ah batteries are connected together in series. The result of this connection is to increase the overall voltage of the system to 24V, while maintaining the same capacity at 65Ah.

Battery Connection Type: parallel (Increases Capacity)

Connecting batteries in Parallel is normally performed to increases capacity. This can be done by connecting the positive terminal of the first battery to the positive terminal of the second battery. Likewise, the negative terminal of the first battery is connected to the negative terminal of the second battery.

When charging multiple batteries connected in parallel, batteries in the string will receive the same charge voltage but the charge current each battery receives will vary until equalization is reaches. Parallel battery connections are used in a number of applications, such as in scooters and UPS backup systems.

Here is a diagram displaying an example of a parallel battery connection:

The above image shows how two units of 12V 65Ah batteries connected in parallel produces an overall output of 12V 130Ah.

Important notes: When connecting batteries together, there are a few important factors you need to keep in mind. It is important to understand the requirements of your application. For instance, be careful from doubling the capacity on your power sport vehicle if you are not supposed to as this may burn the engine.

Always read and follow the recommended guidelines for your application. Never use two different chemistries when connecting multiple batteries together. For example, never connect an AGM battery with a flooded battery. This is because the voltages of the two batteries will be different. More importantly, the charge rates will be different and the capacities may be different, thus resulting in a shortened life span. It is always best to match capacities as much as possible.