How to Connect Two 12V Batteries Together

Be careful when working with multiple batteries.

You may have considered connecting two 12-volt batteries because you need more power in the form of amperage. Or maybe you want twice the voltage. Whatever your purpose, it's critical that you have a basic understanding of electricity before you begin this project. If not, leave the job to the experts, because 12-volt batteries come in all shapes and sizes and some could cause serious harm if handled improperly.

Things You'll Need

• Insulated wire
• Wire cutters/strippers
• Electrical clamps (appropriate size for your batteries)
• Two 12-volt batteries

Instructions

Connecting in Series

1. Research your load to understand the voltage and amperage requirements and limits. Make sure your two batteries are identical. Label your batteries "1" and "2."

2. Choose insulated wire of the appropriate gauge for the load. Cut two pieces of wire that are long enough to connect your load to the batteries and one piece of wire that is long enough to connect both batteries to each other. Strip the ends of the wires.

3. Connect the negative (-) connection of your load to the negative (-) terminal of battery No. 1. Connect the positive (+) terminal of battery No. 1 to the negative (-) terminal of battery No. 2. Connect the positive (+) terminal of battery No. 2 to the positive (+) connection of your load.

Connecting in Parallel

1. Research your load to understand the voltage and amperage requirements and limits. Make sure your two batteries are identical. Label your batteries "1" and "2."

2. Choose insulated wire of the appropriate gauge for the load. Cut two pieces of wire that are long enough to connect your load to the batteries, and two pieces of wire that are long enough to connect both batteries to each other. Strip the ends of the wires.

3. Connect the negative (-) connection of your load to the negative (-) terminal of battery No. 1. Connect the negative (-) terminal of battery No. 1 to the negative (-) terminal of battery No. 2. Connect the positive (+) terminal of battery No. 2 to the positive (+) terminal of battery No. 1. Connect the positive (+) terminal of battery No. 1 to the positive (+) connection of your load.

Tips & Warnings

• Connecting batteries in series means the voltage doubles and the amperage stays the same.

• Connecting batteries in parallel means the amperage doubles and the voltage stays the same.

• Do not attempt this job if you do not understand the risks.

References

• Gizmology: Notes on Batteries
• RVer's Corner: Multiple RV Batteries
• Zbattery.com: Connecting Batteries in Series or Parallel