go, menu, settings, about phone, battery, battery use
The tips below aren't just for battery life, just my suggested settings to hopefully give you a bit more from your DHD:
1. Do a software update - menu, settings, about phone, system software updates.
2. Turn display brightness down as low as you can (I set mine at about 15%).
3. Install something like quick settings and place link on your main home screen, so that you can access quickly to turn say wi-fi and gps on/off.
4. Ensure any sync'ing the phone does, say email / facebook / maps, etc. is as required and not as often as the phone can. Mine checks my email every 30 mins and I don't use GPS unless I need maps.
5. Ensure USB debugging is turned on - this is mainly to reduce lag, but may well help with battery life. menu, settings, applications, development, set usb debugging on.
6. Ensure your phone has a short screen timeout - menu, settings, power saver, screen timeout + settings.
Check out this link regarding a response from htc on battery charging:
Official response from HTC RE: How to double battery Life (WORKS!) + 2nd Reply - xda-developers
Otherwise, it may just be an app that's draining your phone or you might have a bad device.
Try the tips above and see how you get on. Good luck