Samsung s3 Slowly charging and draining fast?

[AC Question]

I've been using this phone for almost three months (that's why It's frustrating me) and about two weeks ago, when I plug the phone up, it takes a few seconds to start charging. It would then charge normally. For about a couple of days though, It will do the pause, then start charging but only increase percents like every ten minutes. Sometimes it die while charging also or just keep a steady percent. Is it the usb port or the battery itself? I've tried different chargers and it gave the same results. Before this, the phone was perfect. I've never dropped it, have an EXTREMELY protective case on it (just in case), and it hasn't been wet at all. I just want to get this problem solved. Really not trying to buy another phone, but if I have to i guess I will.

 

[Rukbat]

1) Charging while the phone is turned on means a slow charge. The phone can only draw a little more current from the charger than it's drawing from the battery. (So, for example, if the phone draws 900mA from the battery and it can draw 950mA from the charger, only 50mA is going into the battery, not the 950mA it seems to be using.)

2) There's no faster way to kill a battery than to constantly use it until the phone tells you to charge it, at about 30% charge or less. You should charge the phone when it reaches 40%-60% of charge. Constantly discharging it all the way gives you as little as 300 charges - if you charge iit every day that's less than a year of use.

3) The second fastest way of killing the battery is leaving the phone in a hot car or other place that's hot enough to be uncomfortable to you. At 104 degrees, the battery capacity will drop to 65% of its rated capacity at 100% charge. Lower that to 77 degrees and you get 80%. (And that'sa from then on - cooling it later won't bring it back.)

Without seeing the phone I can't diagnose the exact problem but if I had to make a guess I'd say it's a bad battery.