While i was searching for my G Wiz i found this in one of the descriptions, Does anyone know if it is true do you need a Master Switch?
The batteries are in excellent condition, and have been maintained by electric boat specialists The Thames Electric Launch Company. The first thing they did was to fit a battery master switch in the supply from the batteries. They diagnosed that the principal problem with the G Wiz is that its batteries run down when it is not being used. This is caused by the DC:DC converter which takes 48V from the main batteries, and delivers 12V to the lights, horn etc. This is connected all the time, even when the ignition switch is turned off. It draws a continuous small current, 0.4A, which does not seem much, but over 24 hours it amounts to 10Ah. Over a week it is 70Ah. Since the batteries are only 200Ah, this means they will be completely discharged in 3 weeks.
Even if you leave them for 3 days between charging up, they lose 15% of their capacity. When this happens, the plates sulphate, ie the lead turns to lead sulphate. Even if you plug the charger in they never recover, so gradually lose all their capacity, even if the car is not being driven.