Charge time excessive?

My iPod Touch 16 GB used to charge quickly (3-4 hrs). One day I plugged it in & waited hours & hours, but it wouldn't charge. Unplugged it, then plugged back in. It charged, but v slowly - the best part of 12 hours. It's been the same ever since - charges, but take a long time.

Haven't charged it much during its life, & have taken good care of it. Is this normal? Is there a reset? Or does it need servicing?

Thanks. Will