Finding a spare 9-cell for T60?

[NJRonbo]

Still thinking of buying a T60 but
need to know a little about the battery, first.

The T60 Duo-Core 14" display comes with a 9-Cell.

If I want a spare, where is the best place to
buy it and about how much does it cost?

(A part number would be an added bonus)

Also, I am guessing the best way to charge
the spare would be to place it in the laptop
overnight plugged in?

Thanks for the help!