I don't like the idea of the side floats. The weight of them add weight and you set lower and they don't balance the front and aft problem you have. I would rather he some how move the battery more forward and not between his legs.
Maybe add some lead weight. I don't know how much his motor weighs but surely not that much, I assume it is some kind of trolling motor. I know a lot of kayakers and they are very particular on how they balance their boats.
Well you take care and good luck on balancing your yak.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978