BatteryStatus shows the status of your PDA’s battery; things like power-drain, temperature and such. And, actually, the “and such” part is pretty extensive! It comes in two versions, a Freeware and an Extended. Both are still free, as in no-cost, but you can do a lot more with the Extended version and it would appear that the author has plans to eventually charge for it. The documentation for both versions is available through that first link but it only contains a download link for the Freeware version. The extended version is available from this thread in the xda-developers forums as is an extensive discussion of it, what you can make it do, and how to go about it.