There are plenty of universal battery packs out there for laptops, they work the same way the universal wall chargers do, you use tips that fit your laptop and adjust the voltage to what the laptop is looking for. They often cost less then a replacement battery from the laptop maker, and have the advantage of working when you change laptops with just a new tip.

They run usually somewhere between $80 and $140, providing about the same capacity as the usual nine cell battery pack 7,000 mah or so.

Google external laptop battery for choices.