JF,
I've used both the Ansmann desktop and rackmount chargers and had issues with both. The desktop units, at $100, had problems making positive contact with the batteries. This was an issue with the batteries as well--the metal they use for the negative post on the battery (and the positive post on the charger) is thin and deforms easily. Often, the battery would not seat and thus, not charge.
With the rackmount, we did have one charging module go bad. Plus, they're $500, which is a lot of money for a battery charger. The AA charging trays for the rackmount version have constant issues staying clipped in, and often times only 2 of the 4 batteries in a tray will charge. It's a lot of money and the stuff should be made better--that's my primary issue.
We made the switch to the Maha batteries and charger and were much happier. The 300 maH batteries put out 8.4 volts and easily lasted two services on our beltpacks (Shure ULX-P). The terminals are made of thicker metal and don't deform. They are also slightly smaller than the Ansmann (closer to an alkaline) and thus fit better in the wireless mics.
The charger is a model simplicity. Just 10 spots to plug in batteries. However, they seat positively every time and charge in under 2 hours. It's worked flawlessly.
My observation is that the Maha 9V stuff is better and cheaper than Ansmann. What's not to like?
Charger:
http://www.thomasdistributing.com/shop/maha-mhc1090f-9v-batt ery-charger-multichannel-smart-9-volt-battery-charger-p-538. html?SP_id=43&osCsid=a98rm8a91donrsllit8gi3gna7
Batteries:
http://www.thomasdistributing.com/shop/maha-9v-300-mah-nimh- rechargeable-battery-p-503.html?SP_id=&osCsid=a98rm8a91d onrsllit8gi3gna7
Note: I don't work for Maha, or Thomas Distributing, nor do I get compensated in any way from either. I just like their products.