Sounds like something a dumb rep would say, but perhaps try loading up a task manager, not the built in one. If it has autokill, TURN IT OFF. That way, it's still a task MANAGER. Use and kill the running apps, then see how long the phone battery lasts. I had similar dismaying battery life on both my D1 and D2G until I loaded one up. Combined with some ending running services. Oh and if you're feeling daring, feel free to kill some system stuff aswell. Things like search applications provider, calendar storage can go. Don't hit anything sensitive sounding though.
Sent from my cyanoblurred D2G