Help choosing battery for toshiba a105 s1712

so I bought a budget laptop, best buy had it for $800 when I bought it and thats not including the tax etc.

First thing I bought it for 400 cash from a friend of mine brand new. Yes he gave me a deal, this was early this year. I loved the laptop except for the battery life, processor and video card, but hey, I dont play much games on it anyways.

At this price, this laptop was a steal, but I am getting sick an tired of having to recharge this thing all the time, the battery is a 4cell 14.4v x 2000mAh battery, recently I been researched and still cant quite think of which battery to replace it with.

Toshiba has two, one being 8cell and other being 6 cell.
heres the link:
6cell
http://www.toshibadirect.com/td/b2c/adet.to?seg=HHO&poid=306454

8cell
http://www.toshibadirect.com/td/b2c/adet.to?seg=HHO&poid=298787

toshiba says the 6 cell can go up to 3.5 hours and the 8 cell can only go up to 3 hours at most. Is that possible? I thought more cells the more capacity.
Also the 6 cells is 10.4 volts x 4000mAh
8 cell is 14.4 volts x 4300 mAh
The only way i was thinking the 6 cell would last longer was because it takes less voltage? Wierd thing is that the manual says the 8 cell would last one hour longer and on the website the 6 cel will last longer. Also the 8 cell is about 70 bucks more.
Too bad I bought a 6 cell, hopefully they didnt mislead me again.. ANyone know through experience which will last longer?
I only paid 50 bucks shipped for the 6 cell cause I got a deal, but I wouldve paid 100 more for the 8 cell if it lasted at least 30 mins longer, as I need alot out of my battery, classes last about 4 hours and I hate having to plug it into an ac outlet. ANy help is appreciated, btw I have a toshiba a105 s1712 model