I have ordered 2 sets of batteries and a charger which I should get today. As soon as I try them I'll let you know.
As far as I know, the 41C was designed for NiCd batteries as NiMH was not available yet and at this time it is impossible to find any NiCd rechargeable batteries. This may make a difference as the characteristics of these two technologies are not identical.
I'm also looking at some batteries to replace those in the rechargeable battery pack, mainly the Varta 422-371 but I need to find someplace that has international shipment options.
Edit 1: Got the batteries (they are NiCd batteries after all), charged them and when I put them in my HP-41CX, I don't get any low battery indication.
For those who may be interested, these are what I got:
Batteries: (NiCd 220mAh) $1.95 each
http://www.batteriesinaflash.com/assemb ... n-top-cellCharger: $26.95
http://www.batteriesinaflash.com/batter ... -batteriesEdit 2: Initially I had some problems with the screen going nuts when doing some operations but after thoroughly cleaning the contacts everything works perfectly now. What's left is to fix my card reader now