PowerGuard monitors the battery status of your Microsoft Windows Mobile/Windows CE powered Pocket PC or smartphone. It monitors several attributes, such as battery current, voltage, and temperature. PowerGuard represents these attributes textually as well as graphically. One can export the measurements to a comma-separated logfile.
The PowerGuard can answer all the questions like how much battery drain is caused by keeping the wifi on.
There are two versions: One is the basic freeware version and other one is the paid version which has the ability to predict battery life and export reading to CSV file format which can be later read on the Desktop.
Go to PowerGuard website to find out more