It's just an external battery pack, that doesn't have a microusb output for power, so would need modding to use with an N900, as it's designed specifically for a beagleboard.
It's also not available yet by the look of it, might as well just buy one of the many many other battery packs designed to recharge phones etc.
One example is the Zagg Sparq, which has a 6,000mAh capacity:

http://www.zagg.com/accessories/zaggsparq.php