I have noticed that my iPAQ 6818 seem to have an excellent battery life, example when full charged in the morning, by evening I still have more than half the battery left even it is ON and doing many things during the day. But I keep reading that other iPAQ 6828/18 users moaning that their battery life is short. I wondered why and I think I know why now!!
It is due to the setting. Just follow mine and see the instant transformation and your iPAQ 6818/28's battery life will never be the same again. See and follow my settings below. Thanks.
P.S. You may think it is a joke, but it works!