Here is a good replacement option for your laptop battery

The Universal Power Battery from APC (American Power Conversion) has a hefty 4700 mAh capacity and weighs just over 2 pounds. The model UPB80 uses the latest Lithium Polymer battery storage technology and has a claimed 8 hour usage time (under certain conditions, of course). Either way, if you are looking for a lot of extra power for those long trips or extended projects or your current battery is close to the end of its inevitable lifespan, this might be a good choice. I believe APC makes a great product (I have used many of their UPS–uninterruptible power supply–products) and their customer service is top notch.