If you can physically take the battery pack apart, you will see that it contains a number of cells wired in series to make up the voltage of the pack. These cells can be replaced - there are 100's of ebay listings. The cells will be a strange size - '3/4 AA' for instance, but every size imaginable is available. While you are at it - use NiMH cells rather than the original NiCd. They will last longer and have little or no 'memory' effect.
Phil Saunders, November 2012
