I ordered a 4/5 AF NiMh size battery as suggested by one of your contributors but when it arrived it was shorter and fatter than the original. The + and - tags were on opposing sides of the battery (one pointing up, the other down) so this was also a slight problem. However, I cut away the strengthening ribs from the inside of the battery holder, cut off the tags from the old battery and soldered them onto the tags of the new battery (providing both the extra length and the tag ends and sizes required to fit into the circuit board slots). Then I bent the circuit board upwards, pushed the battery in, soldered the tags on and it worked straight away! I had to strip the lacquer from the induction coil ends and resolder those because both ends broke away as I worked on the unit. Then I reassembled the unit and used the underneath of the base to turn the bottom of the unit back into place.
Don't know if it's going to charge up properly as the battery came fully charged and I'm going to run it down before trying the charger. If it does not charge then I'm fairly sure it will be because those induction coil wires have come away again during reassembly.
Phil Baker, November 2008