How to Hook Up 12 Volt Batteries in a Seriesby Anthony Smith
Connecting batteries in series is a way of combining batteries so that you can make use of their combined voltage. This is helpful when you have a device that requires a specific voltage that is not that of commonly used and available batteries. An example of this is a 24 volt trolling motor. A 24 volt battery is not something that is widely available, but 12 volt batteries certainly are. Knowing how to connect batteries in series solves this type of problem.
Set the two batteries next to one another, arranged so that the negative terminal of the first battery is next to the positive terminal of the second.
Attach a jumper wire from the negative terminal of the first battery that is next to the positive terminal of the second.
Attach the negative lead from the device you will be powering to the negative terminal on the second battery.
Attach the positive lead from the device you will be powering to the positive terminal on the first battery, and you are finished. These two 12 volt batteries will now produce 24 volts to your device.