As far as powering or charging; I would somehow install a 12v alternator with a voltage regulator inside the car wheel well under fender. Depending on the room I think I would be able to fabricate an inflatable rubber wheel (open to suggestions) to the alternator pulley and make contact to one of the tires (could possible put one on all four, yes it would need flex). As the car is mooving it would be charging/powering.. It would take some trial and error for wheel diameter ect.. Just a thought..
If you think about it, this isn’t a good idea. You would be charging the main pack from itself. I hope you didn’t mean this!
If you mean to charge the SLI (starter, lights, ignition) battery from the main pack, you can do it with an alternator, but you are probably better off using a dc-dc converter, I think, for reliability, or charging the SLI battery whenever you charge the main pack.
If you mean to use the rubber wheel alternator to recharge only under conditions of coasting down and braking, there are better ways to do this as well involving the main motor.