If you find that your battery is discharging a bit too quickly for your liking and you're turning off WiFi, GPS etc in order to conserve battery, maybe it just needs to be calibrated?

XDA forum member vidler found a calibration method that was originally posted on another forum, tried it out and it seems to have worked!  The forum member has helpfully posted the how-to here at XDA.

Results reported so far indicate that the battery stays at 100% for longer and the drop down through 90% is definitely slower.  You'll need to go through a couple of charge cycles, powering off  and disconnecting your Android device from the charger in between cycles.  The sequence only needs to be done once.

It's likely that this method does not solely apply to the HTC Desire, so if you own another Android device and try this out, be sure to report back with your results.

For full instructions, check out the tutorial thread.