I have a Toshiba Satellite L655-s5096. I will like to know what is the battery runtime for this laptop?

I have a Toshiba Satellite L655-s5096. I will like to know what is the battery run-time for this laptop. i am currently getting around 2 hours with it. Is this normal? It has a 6 cell Toshiba battery that came with it. Also is getting the 12 cell battery going to improve the situation? thanks!