I have worked on a lot of w40z pallet jacks the built in chargers were not that good they would go bad after about three years in truck usually the charger would not turn on most were not repairable and very expensive some over thousand dollars at dealer. what l would do is wait till the truck is ready for charge than plug into another charger and let it charge over night untill it shuts off than plug the battery back into the pallet jack and see if the gauge comes back to full if so the charger is bad if not the batteries are dropping down over night and the truck will not reset the gauge. Most 24volt charges will take the charger to about 32volts before it shuts down or about around 11hours than shut off but if the batteries are weak as it sits with no charge the voltage will drop overnight and will not reset the bdi gauge when you plug back in.hope this helps