[MetalMan]

If you buy Dewalt 36v packs the cells have tabs spot welded onto the cells. These tabs can take regular solder and are much easier to solder onto than the aluminum can. They still require a good iron, though.

I came up with something I think would work based on your dimensions, but would probably required a battery tray like the one shown to the right. For material I was thinking 1/8" Lexan/polycarbonate, which is easy to cut and can be bent with a heat gun.