RE: Bad idea # 15
At all costs try and avoid adding weight. It is far better to redisdribute necessary weight. The battery can be realy useful for this. This may sound weird, try taping the battery to a short dowel and laying it in the bottom of the fuselage with the battery at the tail end. if balance is achieved velcro the dowel in place.Ensure there is no interference with push rods.
I know of one racer whose battery was four cells arranged end to end. The battery pack slid into a tube glued to the top inside of the fuselage. The battery pack was slid backwards or forwards to help balance.
Ed S