The stock Dell 1100 MAh battery in my Axim X50v has been slowly deteriorating for months now. It's life on a full charge with typical use has dropped to between 2 and 2.5 hours. This is typical of LiIon batteries' ability to hold a charge, which starts slowly deteriorating after about a year. Exposure to serious heat accelerates the deterioration.
I have a large Mugen 2200 MAh extended battery which I use on long airline trips, but it adds about 9.5mm of depth to the Axim--too large in my opinion for daily pocket carry. I like the quality of the Mugen, so wanted to stay with that brand. In researching a replacement, I found that Mugen makes an 1800 MAh battery (near the bottom of the page). It only adds an extra 2.3mm of thickness to the Axim, comes with its own battery door, and the Dell will still fit in leather cases and its stock case, but maybe not in some metal cases.
Upon arrival, I found the battery to be excellent. It barely adds any thickness or weight to the Axim. Initial monitoring with Uptime 3.4.3 indicates an operating time of 6.5 hours, even with occasional WiFi use. Woohoo! I should have done this before.
For me, the ability to replace/change batteries is a big selling point for Windows Mobile devices over Palms. With my T3, I just kept losing charge until it became unusable. To replace the battery required significant surgery, including soldering with a heat sink. With the Dell, just drop the new battery in and go. Very cool.
Tanker Bob is not just back to fully operational, but way ahead!