You have overcharging, and it is variable. The other posts are good. The battery may not be accepting charge, even if the alternator is trying its little rotor out.

Have a nearby Sears check the battery. Their system reads a lot of info, including dead cells.

I had one experience of killing a battery by driving a hour on a very rocky road. All the stuff on the plates fell to the bottom of the cells and shorted them out. The alternator worked hard, the instrument voltage regulator clicked like mad, the battery heated up, but actually it was dead meat in the morning.

Checked the battery next morning after towing it in. Four (4) dead cells.

Good Luck,

Bob

:>)