The plane should be going on the balance at the same spot...what ever that might be as recommended by the manufacturer. You should not have to move the plane forward and backward for it to balance (i'm sure you know this). If the CG is 3.5" FOR EXAMPLE, put it there and see what happens. If the nose dips down (and the tail lifts), then it's nose heavy and there needs to be more weight in the back. If the tail dips down (and nose lifts) then it's tail heavy and more weight is needed up front.

Move around the battery to fix the problem. Adding weight is always the LAST resort.