New ipod classic batery doesn't charge

Hi, last year i bought an iPod classic, it was perfect until 3rd charge of baterry where it didn't charge no more. And because of out of warranty, i couldn't apply for a replacement, anyway. I went to an Apple reseller store (I live in Mexico) and they offered me to change the battery, I supposed the problema was the battery. They gave me back the iPod with the reparation but my surprice when I arrived home and my iPod still doesn't charge. I called them and I'm going to give the iPod back to be checked. But anyone knows what could be the problema? (it's evident the baterry is not a problema).

PD: i've used different cables, both can sync and appears "charging" icon.