Long-term iPod owners may have noticed that the iPod battery’s ability to recharge and hold its power declines over time.

Previously, owners of a dying iPod had to send the entire gadget to Apple, to be swapped at a price for a re-conditioned model.

Now, Sonnet-Technologies has launched its own line of high capacity replacement batteries, suitable for all iPods except the shuffle and iPod nano.

The kits come complete with tools to open the iPod casing and a step-by-step CD-rom to make sure you do this properly.

Users should note that opening the case will void the Apple warranty.  However, Sonnet argues that the batteries typically start to die after the one-year warranty has expired.