Building a Battery Box

Building a Battery Box

Building a battery box is an excellent way to learn basic fiberglass techniques. No curved surfaces are required, appearance is not critical, and the plywood core forms the mold. 

The figure shows the construction of a box large enough to hold two 12-volt D4s (330 Ah total) or four 6- volt T-105 golf cart batteries (440 Ah total). 

Batteries weigh about 0.75 pounds and contain 2 ounces of acid per Ah. While you are making the box, consider the consequences of 330 pounds of batteries and 28 quarts of battery acid breaking loose in a storm. Also, picture installing or removing batteries weighing up to 165 pounds each.

Steps to building a Battery Box.

1. Mark cuts on 3 ⁄4-inch AC-Exterior plywood. 
2. Apply a layer of fiberglass to both sides of the uncut plywood using epoxy or polyester resin.
3. Cut the panels and apply the resin to edges. 
4. Glue and nail the box together. 
5. Sand around all outside edges and fill inside corners with an epoxy paste. 
6. Apply at least three overlapping strips of fiberglass reinforced plastic (FRP) cloth at each inside and outside corner, making sure there are no voids. 
7. Apply two complete layers of fiberglass cloth over the entire outside and finish with epoxy paint.
8. Fasten the box firmly to the hull with countersunk stainless steel, flat-head (SS FH) bolts. 
9. Apply two additional layers of fiberglass cloth to the inside and finish with white epoxy paint. 
10. Drill a vent hole near the top of the side most convenient to venting. The hole diameter should provide a press fit for a length of garden hose. 
11. Insert  batteries using 1 ⁄4-inch nylon line, leaving the line for later extraction. 
12. Fasten the cover down and run the vent hose to a point outside the hull.