In reply to Indy:
Hi
I recently bought a replacement battery for my 13"macbook
but yours is more complicated and might not be so easy check here, but it is likely to be "non-user renewable"
http://www.everymac.com/systems/apple/macbook_pro/macbook-pro-unibody-faq/m...
or on the apple website
Doubt you can but IF you can swap it out I got a Lavolta equivilent battery rather than a mac one as it was much cheaper and it performs fine - except one thing I don't get a battery low on screen warning before it shuts down on low power.
got it from smart parts sw19 via ee bay
or apple will do it for you for £139inc vat
cheers