"It is always good to have a big battery in a smartphone, so that you can work for longer without having to charge the phone. Larger batteries often mean a larger overall size, which isn't for everyone. However, sometimes the need outweighs the shape, aesthetics and weight of the product. So if this is the case for you and you own a HTC HD2, this extended 2300mAh battery will be ideal. An official extended battery for the HTC HD2, this 2300mAh battery comes complete with a replacement back cover, that has a kickstand (allowing you to stand the device up - perfect if watching a film)."
It adds significant bulk to the HD2, but it nearly doubles the battery power, so if you're using your HD2 as a portable entertainment system on a long flight, this would make a great solution. Leigh Geary from CoolSmartPhone has snapped a couple of real-life photos as well. I wouldn't use this often, but it would be great to have for the times I needed extra battery run time.