If the car has a 48v Power Drive Charger it will not switch on if the battery pack is below 32-34 volts. If this is the case you need to bypass the charger relay. Disconnect the charger both AC and DC. Remove the charger cover (eight screws) Locate the black wire that goes from the AC circuit breaker to the relay and disconnect from the AC circuit breaker terminal. Insulate the loose end so it does not touch any other component including the case. Disconnect the wire from the transformer to the relay, at the relay, and connect this to the open terminal on the circuit breaker. The relay is now bypassed. Plug in the DC cord to the car first then the AC to an electrical outlet. The charger should begin to charge. Allow to run for one or two hours then disconnect the AC cord first then the DC cord to the car. Return the wires to their original positions, replace the charger cover. Plug in the AC then the DC and allow charger to run until it switches off automatically. If at the outset your batteries are above 34 volts then this procedure will not help and there is another problem possibly the OBC