My mother has had a few stay away from the big heavy ones. She is 14 stone and uses the little collapsable ones with a single deep cycle lead acid battery. Weight of the buggy is the determining factor as well as battery quality for how much use you get per charge. The small wheel ones are fine for tarmac use but do not get a 3 wheeler. Even the small ones are heavy they pack fairly well in the car but boy they can knacker your suspension, add the shopping as well if thats going to be a use for it and it s quite a load on the car.
Look for the ones that break the motor and rear wheels away in one unit, they pivot and lock in with a release lever and rock back to seperate.