We use nothing but Dells here and if weight is not an issue would strongly suggest staying away from the 4 cell battery. The 6 is ok and the 9 will give you the most battery life. If you are going to be plugged into the wall most of the time or weight is an issue then adjust accordingly. As with most laptops when running on batteries time fluctuates on power setting on the machine and what you are actually doing on the machine, overall they seem to hold there charge and last quite a while. Hope this helps.
Drew