iPod Touch 3g will not charge

Hello there

I recently fixed an old iPod Touch 3rd gen. 64 gb where the touchscreen was not responsive. After fixing it, I was able to update the firmware to 5.1. Previously the firmware was 5.01 Right after that, the battery was not charging. The indicator in iTunes and on the screen itself were showing the battery life decreasing and a couple of time it warned me that the power was below 20%. I immediately connected it to a USB port to recharge it. Unfortunately, it did not work and it slowly used all the charge in the battery. iTunes does not recognize it anymore. So , I opened it up again to check the battery voltage. To my surprise, the battery voltage is 3.3 V and if I press the power button , the battery icon with the the red mark on the left shows up, but no matter how long I leave the iPod connected, it never improves the charge. Has anybody else experienced the same problem, I mean right after the 5.1 upgrade and any solution to this.

Any help is appreciated.

Thanks

Massimo