The position of the batteries depends on each vehicle, the need (last kilometre or be sure to make Paris-Deauville...) and the possibilities of the current batteries (size, capacity in kWh... they will evolve and become miniaturized in the future of course). Care must be taken to respect the integrity of the starting vehicle, and to distribute the new masses to adhere to the starting configuration (with which the vehicle was originally approved). A secure battery pack, with a high standard of tightness, will replace the tank, but if you want extra range, you can add some in the boot or around the engine. In any case, the batteries will never be in the passenger compartment.