This was done years ago:
84V Upgrade to my ZAP Truck - Endless Sphere
It was also done somewhat later with this result:
The burned vehicle, AIR, had a switched-in extra boost battery. I think it had a switching system not rated for the voltage(a real no-no), problems with a dead short from a bad switching sequence, or a combo of all of the above- probably exacerbated by poor fusing.
You'll probably be ahead of the game by just buying a beater Leaf. These ZAP vehicles were, AIR, pulled by NHTSA because of poor braking performance. I ended up with the burned one. I kick myself for passing on a set of Lancair wings that I would have attached to the burned carcass . Not to ever fly, but to mess with pilots and drones flying over my bone yard!