I won't pretend to understand the full details of batteries, but from what I've read in passing over the last few years, it sounds like heat and the voltage you charge to are big factors in battery life.
Supposedly for modern batteries the best way to lengthen their life is to not fully charge them. Some laptops allow you to set the bios to cut off charging at around 70-80% of capacity. Obviously if you're off on a trip, top it off first
The battery on my main laptop used to last between 2-3 hours, I now get (4 years later) around 20 minutes out of it. Shame I didn't know about keeping it at 100% not been the best of ideas
Still I very rarely use it away from the mains, so that 20 mins is great, it's a little UPS :P
edit: couldn't find any of the original articles I read it in, but here's a post which covers roughly the same info
http://www.cultofmac.com/147994/gett...t-i-os-x-tips/
edit2: I wish every company would make batteries replaceable, ideally user replaceable, but even if getting the casing off the laptop and undoing dozens of screws is required, as long as the battery itself is not soldered or glued to the board I'd be happy.