Racing battery question

LOL. The reason the right rear drops is that's the side the torque tries to pry off the ground with axle / suspension torque, and since the machine cannot "pick itself up" the next best thing is to pull the body down on the axle. Anyway you look at it, on a non- limited slip axle, the right rear is nearly always the one tire which spins.

Putting more weight on the left side is not gonna fix that.