Achance

Does anybody know where I can find an extended life battery for a dell 8100. For a 2nd internal battery it costs about $140 and I know they make external batteries that last alot longer for a little bit more $$. The only brand I could find was called Powerbase and it looks huge and weighs about 4lbs plus it isn't Li-ion. Does any know of another brand, That might be smaller and weigh less? It would suck to have to lug that thing around with my computer that already weighs a ton.