ill take a pic of the parts i am talking about.. but basically youll end up with two loose wires like this
|_______________| a wire with a thin metal tab on each end. then you take one of of the wires and attach them together to make a tab u can slide in between the terminal and the batt.. insulate the backs so they dont contact each other.. now take the other ends and use electical tape or shrink wrap to secure them to the second batt. no risk of heating the cell and frying it. and no perm mods done to your chassis