How to Wire Twin Batteries in a Boat
Twin batteries need to be connected in parallel in a boat, meaning the positive terminal from the first battery has to go to the positive of the second, and the negative to the negative. This will keep the voltage the same, but double the current, both for running auxiliary equipment while stopped, and also when charging the batteries. Adding a switch or an isolator may be more convenient, but it is not necessary. For temporary applications, use auto jumper cables if the second battery is close enough.
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Things You'll Need
- Battery cables
- Wire cutters
- Knife
- Screwdriver
- Wrenches, size of battery terminal connectors
- Electrical tape
- Safety goggles
Instructions
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1
Position the second battery in a convenient location and run the cables from the first battery to the second.
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2
Tape the cables for safety at the first battery end.
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3
Strip the cables and connect them to the battery at the second battery end.
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4
Remove the existing cables at the first battery end and strip and join the new cables with the old in the new connectors, then connect them to the battery.
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Tips & Warnings
Use red wire for positive and black wire for negative to better identify them, especially if the run is long and you can't see both ends of the wire at the same time.
You may want to install a selector switch to use either battery or both, or add an isolator to keep from using up both batteries and getting stranded.
If using jumper cables, observe polarity, and when making the first connection, be sure the other end of the jumper cables aren't touching.
Make sure there is no gasoline or fumes where you are working, as sparks could cause a fire.
Wear safety goggles when making connections. Arcs could cause flying molten lead or copper.
Make sure your charger can handle the current of the second battery. Consider that it will be double. You may have to disconnect the batteries to charge them separately. Check with your boat manufacturer for details.
