Highest capacity 8cell battery?

[mtbiac]

I'm looking to buy the highest capacity 8 cell battery possible. I bought an aftermarket 8cell on eBay for my X41 Tablet, and its listed as 4500mah, like the standard IBM extended 8 cell battery. HOWEVER, in power manager, it lists the battery's "original/intended" capacity as 6300mah!! It had 0 cycles when I got it, bought it NEW from a very trusted eBay seller.

so basically, I'm wondering if its possible to buy say a 5400mah+ 8 cell battery for the X41 Tablet? If so, where? I know I can buy that extended battery for the bottom of the laptop, but then it gets to be way too heavy

thanks much!