[Liverpool] External universal laptop battery

[Sebastian]

Anybody here has any experience with these universal batteries (or similar):

http://cgi.ebay.co.uk/Universal-External-Battery-most-laptop-/130481566861?pt=UK_AudioTVElectronics_Video_DVDPlayers_Recorders&hash=item1e614eb48d

At 75Wh - two of them should give me 10 hours of work on my laptop (and 
a hernia from carrying them :-) ). If anybody has one of these - I'd be 
interested to hear how they fared.

Also - I don't understand why does it have to weight 1.5Kgs. My laptop 
battery is 57Wh - and the whole laptop barely weighs 1.5Kgs.

Thank you,

Sebastian