I`m going for a plane trip (4.5 hours) and wanted some extra juice for my N900.....I though why not take an external battery with me....problem is that the external battery is 1800mA@12V so need to convert that....so, I`m looking around found a car charger ( output 5.5v) so it`s just perfect, now I need a wire going from the battery to the car charger (check), then I need a male-to-male adapter to go from the car adapter to the Nokia adapter (check), then plug my N900 in.....IT WORKS!

Voila!.....hopefully the airline won`t think that I`m a terrorist trying to trigger a bomb....ahaha

http://cgi.ebay.co.uk/12V-1800mA-Rec...item27af0f594c
(This is a similar battery on Ebay...and its only 22 pounds!)