Even if you could it would be pointless unless you had a bad batter already. It would probably get the same time as your battery originally did if you put in in your 2009 MacBook Pro. The reason the new MacBook Pros get 10-hour battery life is because they have a less power hungry CPU and integrated graphics. This allows for a lot less power to be used. If you took the same battery and put on in a 2012 MacBook Pro and one in a 2009, the 2009 model wouldn't get a 2012 model's battery time. I think that physically you can do it but I don't think that there has been a sizable increase, if any, in the watt-hour's of the new batteries.
Hope this Helps
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