I am not sure what those registry keys are for for sure, but you can find a way to toggle the battery warning popups by adding a key to the registry. You can find details here:
http://www.phm.lu/PocketPC/RegTweaks/Tweak.asp?ref=55
There are also other tweaks that can be found here:
http://www.phm.lu/PocketPC/RegTweaks/