Battery benchmarks tend to err on the side of casual use, offering higher numbers than many of us actually get on our laptops. If you want to know how long your battery will last under a strenuous workload, the popular Peacekeeper browser test can give you a good idea.
The Peacekeeper test checks browser compatibility and speed by performing a variety of tasks, some more CPU-intensive than others. While most of us won't ever use our laptops at nearly full blast for the entire duration of their batteries, when you buy a laptop you don't just want to know the battery life you'll get from casual use, but also the minimum on offer.
The Peacekeeper test, which lasts about five minutes, can run itself on a loop until your battery dies. When the process starts you're given a code that you can enter when you finally boot your computer back up to see how long it lasted.
If you want an accurate picture of how your battery stacks up under pressure, give it a try. Scroll down to the bottom of the page where they hide the battery test link to get started.