Wilderness BD24 Bike

I have a Bd24 brushed kit I have had for about 3 1/2 years and it worked fine until recently. After finding out the battery was disconnected I hooked it up and I'm not sure if I need new batteries or brushes in the motor. This is what it does. Everytime I hook the charger it is always green now and today the wheel turned for about 20 seconds then I heard a pulsating noise coming from the hub motor on and off when lever was pressed down. Even though its over three years old there are little hours on the unit. Can you tell me what you think it might be? Thanks...