I don't have a 12-cell laptop battery, but I just wanted to point out that there's cells and there's cells. The energy storage capacity of different "cells" used by different manufacturers varies widely, as does the current draw by different laptops. A 17-inch "aircraft carrier" laptop is going to consume a lot more juice than an Atom-based 9" unit with an SSD. Hence, their runtimes on a "12-cell battery" will be hugely different.
For what it's worth, I used to have an Asus 1000HE which ran for almost 10 hours on a 9-cell battery (Windows 7), before it was snatched away from me by a family member who was quite happy to resort to underhanded hardware acquisition tactics.