First of all, why are they trying to use two different battery packs?
For hairball ideas, I thought using a
motor for the rear differential was worth researching. If you thought 38lbs was bad, this motor is 150lbs. But it's 33kw continuous. To get the nominal battery pack voltage to 312volts I was looking at 26- 20amp/hr batteries. I found AGMs with 12amp/hr and 18amp/hr. But even 20amp/hrs would only be worth 10 miles@60mph at 50% DOD and still weighs in at 400lb battery pack for lead acids. The lithiums would be 200lbs and $7000. It would work in a full size sedan or a compact pickup like my ranger but it would require a 70hp motor/generator which is about what the newer 1.0L Metro engine do. But I haven't found an inverter.