When I got to class, I realized there was a spot of melted deformed plastic on the back of the case behind where the fourth battery slot is. After taking it apart and seeing no obvious damage to the circuit board, I left it on for a little bit. Just as I thought, as soon as it displayed "bad battery in slot #4" I checked the circuit under it, and a component was heating up abnormally. My hypothesis is that as soon as that part heats up, the charger detects it as an overheating battery and shuts off. I'm sad to see this charger go, it worked really well.