iPhone battery dies after one day

Hey guys, weird stuff has been happening with my iPhone I’ve had my 3GS for over a year now and it has always worked normally. Then a couple of months ago I charged it with a power charger, but instead of getting charged the battery just seemed to get sucked out of it. Now my battery won’t last longer than a day.. What the heck? Anyone has this problem?

When you plug it in (to charge) does it recognize it?

Yes it does. Everything works just fine, only my battery gets drained.

Have you done a hard reset (hold power and home buttons until the screen goes blank and the apple logo returns, then release the buttons)? It's a generic solution, but my battery has given my problems before and that seemed to fix it. One time my battery went from about a 70% charge to flat dead almost instantaneously, and my wife's did the same thing once. We plugged them back in and did a hard reset...it hasn't happened since (knock on wood).

Something else to check on is whether or not you have tons of apps running in the background. Location/GPS based apps are especially draining.

Yes, I did the hard reset already a couple of times.. and so far as I know they're no apps running in the background. My iPhone gets superhot at times too... can't be good