Build a compartment on the opposite side of the box from the fuel for the battery. This will help balance the box when carrying. It's a nice job.

Our field-box is similar with the exception of the battery compartment. You'll notice the 1/4" screws sticking up through the top of the compartment. The battery is connected to these screws, which I attach my field charger and starter to for power. I also charge the battery via these screws. I have Velcro on the battery to keep it from moving around inside the compartment. I didn't think an expensive power panel was necessary and I wanted to keep it simple so thew screws worked out nicely for me.