Where to buy 9 cell battery for T400

[lagoausente]

Hello, finally decided to buy a used T400 on ebay. I had good luck in the past with 9 cell battery from ebay for my old T40, but had a bad experience with a battery for my acer aspire one, so I´m looking for advice.
I know original ibm batteries are more reliable, but price is much higher, does it woth?
Any ebay seller that you should recomend?

Thanks a lot.