The on-board battery charger can take up to 8-9 hours to fully charge the battery(ies). It has to go through a full cycle. If you interrupt the cycle (unplug the charger), it will have to start over.
There are indicator lights on the panel of the battery charger showing how much the batteries are charged. The first part of the cycle charging usually goes pretty quickly, and the last part can sometimes seem like it’s taking forever. Keep it plugged in and let it finish to fully charge the battery(ies).
