Apc and a few other companies have made in the past a battery the size of a 14" laptop and it comes with 20 different plugs for laptops. I own one that runs my 15" laptop for about 4.5-5 hours before using the battery on the laptop. There is also a smaller one capable of about 2 hours. I bought mine from Circuit City before they closed for about half price but you should be able to buy them elsewhere for around $100-120.
here's one on ebay
a different style
a different one on tigerdirect.com
Just look around for universal notebook battery
-Mike AA