How to Install a Marine Battery Box
This article shows how to install a marine battery box in your boat according to coast guard regulations.
Batteries… we all need them. In order to install them properly, it’s important to comply with coast guard regulations. I recently installed two Group 31 deep cycle AGM batteries on my 27 US Yacht sailboat, Solace. I was careful to comply with the coast guard regulations. Below is how I did it and how I recommend you do it too.
As my sailboat has a pull-start outboard, I don’t have to worry about a starting battery. However, most boats that do have starting batteries will need to install two (or more) batteries – one for starting and one for ‘hotel’ loads. The ‘hotel’ battery is usually a deep-cycle battery used to power your anchor lights, and other long-term electrical loads. Two-battery installations are probably the most common on boats 32 feet and under, so the installation below will be applicable in most cases.
Boat Battery Box – Coast Guard RegulationsThe official coast guard regulations for installing batteries require that the batteries are secured against both horizontal and vertical forces so that it can’t move by more than one inch in any direction. Additionally, there are regulations that state that the electrical terminals must be covered by a non-conductive material. This can be a rubber terminal cover or the lid of a plastic box. The best marine battery box I’ve found are plastic battery boxes with a tie-down strap. So long as the box is secured to the boat, this will meet the coast guard requirements.
Installing the Marine Battery Box
I was lucky that my boat had a shelf in the engine compartment made of fiberglass-over-wood. This meant I could safely screw into it.
Note: Do not screw into your boat hull! That is a bad idea and you’re just asking for your core to rot out. If you do not have a convenient shelf to mount to, you can fiberglass one in. This is extra work, but it’s well worth it. Check out my articles on how to work with fiberglass for more info. This is also a really good time to patch up any holes you find in the fiberglass or other areas of the boat. For a quick, easy fix you can use a marine silicone sealant. However, it’s always a good idea to go the extra mile and repair any problems with the gelcoat.
Properly securing the battery box to the boat is the most critical part of installing the batteries properly. I can’t overemphasis how important this is. This not only ensures that you’ll comply with coast guard regulations, it is also one of the most common ways I see boat owners damage their hulls. People in too much of a hurry, screw directly into their hull, which eventually leads to dry rot in the fiberglass core. Take the time and do this step correctly.
In my case, I used 3/4 inch long, #6 wood screws with a washer. I installed four in each battery box. The first time I secured the boxes, I forgot to install the strap. I had to remove the box and reinstall with the strap underneath. While I was at it, I squired some silicone sealant into the new holes to seal the screw holes and prevent moisture penetration. It’s always good to be wary of moisture penetration into the wood core of any fiberglass.
Since I only have one battery bank, I wired these two batteries in parallel. Once all the wiring was done, I installed the lids and tightened them down with the straps. The screws secure the box to the boat. This ensures that the marine battery boxes comply with the horizontal force part of the coast guard requirements. The plastic lids comply with the part of the requirement of a non-conductive terminal cover, and the strap ensures that I meet the vertical force requirements.