1: Basically, the battery is about to break, the electric vehicle charger to charge the battery using the first constant current and then constant voltage method, the battery voltage slowly rises during the charging process, and finally reach the constant voltage value of the charger (the charger shows that the charge is full), the current becomes very small. If the battery is at the end of its life, the charging voltage rises quickly and reaches a constant voltage value, so the charger shows full, but the actual charge is not much.
2: The low constant voltage value of the charger is also a reason
Borrow someone else's charger just like yours and try the elimination method