I have a 5000t with 12 cell. At max brightness with the glossy screen.. I get just about 5 hours.
Thats with the processor 1.85 GHZ duo core. Power setting set to desktop/max.
I have both the 6 cell as well as the 12 cell. I like the keying position of the 12 cell best. Its Angled like a stand alone keyboard used by desktop. When watching DVD at "Bedtime"... I prefer the 6 cell (for I dont often finish the dvd, and its not as shameful to run battery dry only a 6 cell. I pop in the 12 cell in the morning).
However, PCMAG got 7 hours.http://www.pcmag.com/article2/0,1895,1949638,00.asp
Since I never use brigthness less than max with power setting at notebook/portable level
I have'nt confirmed if 7 hours is possible.
12 cell on your lap is BEST. It allows airflow and your body heat dont warm the laptop as much. Certainly not choke the vents.
BTW... this battery as shipped from HP or Costco via HP is not a RECALLable battery.
SO not the worry of flaming your pants and "Parts".