I have a model 890 room a it hasn’t been used in over a year because it was in storage now I can’t get the battery to charge. Before I buy a new battery I wanted to make sure the charger was working. When I plug it in the green light on top comes on but as soon as I put the room a on it the green light goes off and stays off until I unplug the charger and plug it back in. Is this a issue with the charger or a safeguard because the battery is worthless now?