I have a similar issue, one battery out of my 3 is always charging, had the charger replaced under warranty (not because of the issue, one of my leads melted) , same issue, so its obviously the battery. Doesnt make much sense though because after 6-8 hours of charging, if i take a volt meter, the one battery shows 12.69v (tested it 24 hours after), its only 2 years old.