Is this battery problems or charger or phone?

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http://forum.xda-developers.com – So one day, I was left at my friend's house without my normal, Sidekick Charger. My friend had an HTC Sense charger and it seemed to fit my Sidekick, and without thinking twice, I used it for the night. My phone charged ti 100% and I unplugged it and used it throughout the next day. It died and I tried charging it with my normal charger and it would randomly stop charging and continue charging and then stop and repeat. It's gotten worse the past week to the point I can only charge it halfway at night. I'm running on the new GOV32 if that helps. And I'm using the normal Samsung charger. (HowTos)