Best to Not Move the Batteries

Posted: September 1, 2012  |  Tag: Generators/Inverters/Batteries

By: John Temple

On my 33-foot powerboat, the four house batteries are in the engine compartment at the very back. Would it be a good idea to move them forward under the cabin floor, which is closer to the inverter and the power distribution panel. The main benefit is to move all that weight forward. They are the flooded type. Is there any danger from fumes in the cabin? 
Having your batteries in the engine compartment is a good idea. Engine compartments are made to take care of fumes and douse fires. Not knowing a lot of details about your boat, my first thought is this: If you want weight forward, move the batteries forward within the engine room. Batteries can gas, especially if they are flooded lead-acid types, and their gas is explosive. Engine rooms are vented and often have exhaust fans. There is a danger in having fumes in the cabin compartment.

If you changed to valve-regulated lead-acid (VRLA) batteries such as gel or AGM, I would feel better than I would about batteries that can release fumes into the cabin. However, even VRLAs can gas. Flooded lead-acid batteries release gas when charging and also when equalizing to “clean” the plates. If you need to replace water in the cells, it is because they are gassing. That is normal and, again, not good in a cabin space. Older AGMs can benefit from equalizing, and even they can gas.

Before moving any batteries into an area that vents into the cabin space, I would suggest contacting a battery expert who will survey your specific application, or have a surveyor approve the installation for safety and adherence to Coast Guard regulations.

Instead of moving the batteries to get them closer to the inverter and power distribution, do it “virtually” by increasing the battery cable size. If it is a weight-distribution issue for performance, this is a complicated evaluation. If you are not certain about whether weight distribution will truly help performance, consider just emptying the water or fuel tanks aft and putting weight forward temporarily (or just move those batteries temporarily on the floor for a test), and check performance changes before doing anything else.

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