The HTC DIAMOND does not win any awards for its battery life. Let’s face it, even with average use, you won’t be able to last a full day with the stock battery, which has just 900mAh juice. HTC chose style over function on this device and I support their decision. Here is a picture of the extended battery sitting side-by-side with the stock battery.
Here is another one:
[xda-devs post] [pocketpc.ch blog]