8 cell battery, best price and ultrabase x6 fit

[moijk]

I got a ultrabay from a x60 user which in most searches result in beeing described as x6 tablet version - but it still fits my x61s well. The product p/n is 42W3107

I'm wondering about buying a 8 cell battery, and on ebay almost every battery is of other brands with slightly to very different looks. so my question is if anyone could point me to a cheap, powerful, realible battery option anywhere on the net which ships to Norway and fits my ultrabase?