This sounds like it might be a problem with the battery charger port or its connection to the controller or wiring harness. I would test for Voltage at the charger port to see if it is actually connected and making contact with the battery pack. If there is no Voltage at the charger port then it may have come unplugged from the controller or wiring harness, or it may be faulty and need to be replaced.
The problem could also be with the charger, so I would also test the Voltage at the charger's output plug to make sure it has output Voltage. More than likely the problem is with the charger port or its wiring though.