RE: waiting for my zoe and looking for electrical details
Roger, welcome to the forum.
However, I don't think your idea for range extension is workable. Li Ion batteries are very expensive, which is why they are leased with the Zoe. Also, the energy stored in a charged battery pack is similar to the energy in a full petrol tank, so carrying a charged battery pack on the back seat is similar in risk to carrying petrol cans on your back seat - arguably it's worse, since batteries can supply their own source of ignition through sparking. That's why car manufacturers go to great trouble to incorporate them into the design of the car, usually in a compartment separated from passengers, inside a reinforced cage, and fitted with emergency shut-offs.
Given that the Zoe has the longest range of any electric car (except the Tesla) I wonder if you really need more range. Certainly hills aren't necessarily a big issue since regenerative braking will help you gain downhill a lot of the energy you lost going uphill. Your requirements may be better served by fast charging.