Relating to grounds and dual batteries does no one hook them up correctly for parallel batteries (hot from passenger side with existing wire, ground only from drivers side with both neg cables in series to starter, rest of loads to fender solenoid (of course jumper to solenoid from starter or pass side + and from center ground point to ground on starter). This ensures both batteries share all loads equally if battery to battery wires same gauge. No more one battery hidden failing and dragging other down until they both fail. No more differences between battery voltage loaded or not. Works for high current ebike batteries which are sensitive in parallel situations so should work here. Will let you know after I finish crimping and moving mine.
I didn't fuss over anything, I just hooked them up the way the factory did. You make a good point though.