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I own a Macbook Pro Penryn (3.1) 15", one like this:
http://appledistrict.com/wp-content...cbook-pro-15-inch-penryn-review-1-300x270.jpg
The battery died today after 4 years and some months of life, otherwise it works still great while plugged to electricity.
Is this the correct battery to replace the dead one? (I suppose so)
http://store.apple.com/it/product/MA348G/A
Thanks.
Apple - Batteries - Battery Replacement

This should answer most, if not all, of your battery questions:
 
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