Sony Viao Laptop Battery Question?

I will purchase the sony vaio vpceb390x laptop from sony.com. I heard theSony Laptop Battery life for this laptop is pretty poor. Its a 15.5' laptop by the way. It says it gives 3.5 hours but most people say its about 2 hours. My question is this. I see they sell a Laptop Battery for it on their website that gives 5 hours. I would guess 5 hours would mean 3.5 at the most if 3.5 hours on their regular battery gives 2 hours max. Does anyone know what is average battery life for a 15.5 laptop these days? I mean i don't think there are many 15.5 laptops that are longer than 3 hours battery life correct? I think the only exception would be the macbook pro 15? Even the dell studio 1558 i heard was 2 hours.



I see there are many ebay sellers that sell laptop batteries such as for dell laptops for 50-75 dollars whether 6 or 9 cell and they have very high ratings. I know if you buy those laptop batteries from dell's site, it would cost you minimum $100 and might be $200 or more. My question is, would it be possible to buy a sony laptop battery on ebay for this specific sony vaio vpceb390x laptop? I see many sony laptop batteries but they don't seem to be compatible. Sony sells the longer life battery for it but it cost $200 and i think that is pretty pricey and want to know is there anywhere else i can get it for cheaper? Can I buy the Toshiba Laptop Battery?