I fly internationally at least once per quarter. Given that flight time tends to be some of my most productive time, I need to ensure I have enough juice to get me over the Atlantic without missing a beat on email or, even more importantly, that Arsenal match I previously ripped to my Mac's hard drive with Elgato's EyeTV 250.
I used to use Electrovaya's PowerPad, but it doesn't (or didn't) support the MacBook Pro. So when I started looking around for a replacement, I discovered Batterygeek's Portable Power Station. It's bulkier than the Electrovaya battery, though more compact, and doesn't last as long (eight or nine hours, depending on how CPU-intensive my activity, compared to 10 to 14 hours). Having said that, Batterygeek has come out with new models that last as long, if not longer, than Electrovaya's (one goes for over 20 hours).
Operation is simple: plug in your laptop and work (or play) for hours. The batteries are pricey (at least $300 for a decent one and up to $900 for the longest-lasting ones), but worth it. I suppose it depends on how much your work is worth to your employer, but nine hours on a plane eating peanuts and watching Evan Almighty for the tenth time is not a good use of my time, or my employer's.
Get the battery. Batterygeek's service is impeccable and the product works great.