From HP I got this interesting background information on the battery life issue of the HP Jornada 928 WDA and how to enhance it.
Some customers have experienced a shorter battery life of their HP Jornada 928 WDA than expected. This is mainly due to the usage pattern of the device. The reason for this is the usage of the active cover that, as what customers seems to don't know, doesn't close down the PDA but only suspends the screen but keeps the system alive in the background.
A way to fully optimize the battery life is, every time you stop using the PDA-side of the product is to power-off the system by pressing the power button before you close the autocover of the WDA. This will bring your battery life to highest performance with or without the radio being switch-on.
If you would like to keep using the autocover and not have to press the power-on button every time then battery life will be affected but this can be minimized by going in the HP Settings program and adjusting the System standby time on battery power from the default 5 minutes to 1 minute as well as to change the backlight settings to 10 or 30 seconds. This improves the battery performance of the WDA but the optimum way is still to close of the product after every usage with the power-on button.
Cheers ~ Arne