Futuremark, the maker of the 3D Mark and PC Mark computer benchmarks and the Peacekeeper browser benchmark have released the Powermark battery life benchmark. A standard feature listed for any laptop is battery life, so it is also a standard test for laptop reviews. What Powermark does is try to simplify the battery testing process while also keeping it comparable to what an average user would put their laptop through. If you feel the Balanced, Productivity, or Entertainment options are not accurate for real-life usage, Powermark also allows one to put together a custom benchmark cycle. Browsing, gaming, video, and word processing workloads can all be manually set to whatever weight someone wants them to have during the testing cycle.
This software is not meant for the average user though, with its professional license costing $200 for ten activations. (You have to request a quote for the Enterprise license with unlimited activations.) Not exactly a viable way to confirm your laptop is getting the life it should according to the box, but it could be what is behind the numbers you see for reviews of Windows 7 portable devices.