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Yep, what everyone else says, take it to Apple. You never know, you might get lucky and get a generous Genius who won't charge you for the replacement!

As far as your newer MacBook Pro, get AppleCare. From what all I read about it, the battery was probably about 95% of the reason that I bought AppleCare with my new MBP. I LOVE this thing!
 
Ask a apple service tech today when experiencing the same issue on a customer laptop. They replaced free of charge out of warranty. It's up to them, but they usually do.
 
Mine (Late 2008 unibody) had almost the same deal, it was bloated so much the bottom casing could barely hang on, It was out of warranty, so they gave me a choice between on off the shelf with a 1 year warranty for $129, or a Genius replacement for $99 with a 90 day warranty.

I got the $99.

But I have heard of others getting free replacements anyway.
 
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