That's an interesting idea, although I think it'd be hard to make a piggyback battery pack light enough. The Tesla's swappable battery pack module including fra

That's an interesting idea, although I think it'd be hard to make a piggyback battery pack light enough. The Tesla's swappable battery pack module including frame/supports, armor, and coolant weighs over 1,300lb. Nobody wants lithium batteries in their passenger compartment, but I do suspect it might be possible to make a ~200lb pack that would fit in a Tesla's frunk and move it at least a few miles. Thermal management would be a tremendous challenge in that area unless the "auxiliary battery" port could somehow interface safely with the car's existing liquid cooling system.