The battery box is a finished steel box that Van's sends already powder coated...and then they tell you to destroy it. The plans call for 2" holes to be drilled in the box. These are just optional lightening holes - 4 in the front and 4 in the back. My 2" hole saw proved to be fairly worthless the other day when I was trying to drill through the firewall, so I just decided to go with 1 1/2" holes instead. That hole saw was new and worked a lot better. After drilling the holes in the front side, I decided not to do the ones on the back side though. Cutting into thin steel sheet like this leaves terrible ragged edges on the exit side of the hole. In order to clean it up I had to grind the edges down and then hit it all with sand paper. At that point, the nice powder coat wasn't so nice anymore. Knowing what I know now, I wouldn't have bothered to drill any of the holes. Sometimes saving that 1/10 of an ounce of weight just isn't worth it.
I also made the battery hold down strap. It's a 1/8" thick aluminum bar. For this one I did go ahead and drill all of the lightening holes. Aluminum is a piece of cake to work with compared to thin steel, so these holes only took a few minutes with the unibit in the drill press.
The box attaches to the firewall stiffeners and bolts replace a couple of rivets. I drilled out the existing rivets in the firewall and upsized the holes for bolts. I also made two 7/8" spacers that go under the hold down strap.
