Wirelessly posted (htc Vogue: Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; IEMobile 7.11) Sprint MP6950SP)
There is a freeware app called battlog that will monitor voltage and save to a log file. That will show you what is happening. It requires NetCF3.5 to run. It's not new but it would do the trick.
Get it at:
www.pocketpcfreeware.mobi
Good Luck!