Based on Raphael Wimmer's blog, I replaced the rechargeable battery and recorded the procedure.
Finding the NiMh-Battery seems to be difficult. If you live in Switzerland try
http://shop.contrel.com/downloads/PDF...
Contrel AG in Hünenberg is a possible source. Or Conrad Nbr. 255032-62
Batterielieferant, der Link oben.
(Update 21.7.2012)