Weird thing happened to me last night. Left the phone charging overnight. It wasn't completely dead. I think it had about 30 percent battery life. When I woke up it was at 68 percent. Must have been on the charger about 8 hours.
That same thing happened to me. After 2 days of trying to figure out why the dreadfully slow charge, I took the charger back to sprint for a new one.
They tested it, and said it was fine. I told them ( again ) it wasn't fine.
So they plugged my phone in and said "Look, the charge icon is on". I was like "ok wise guy.
I'll give you $10 if the battery % increases in the next 5 minutes. If not, you get me a new charger and stop bustin my balls"
5 minutes later I walked out with a new charger.
The guy told me this was the first charging issue he had seen.