It probably has corrosion under the charging ic. You could pull the chip off and clean it and reball it and put back on. You could also try cleaning the board in a sonic cleaner with Branson ec cleaner and dropping it in alcohol and blowing all of the moisture and alcohol off. Or you could take it to a repair shop and have them repair it. Or last option you could buy a new set of them. Unfortunately it probably will cost more to repair them than to replace them. If you have access to a sonic cleaner and the chemical to do it that's what I would try.