A friend of mine just got a nice deal on a MBP 15", but the only issue is that the battery needs to be replaced. Where is the most reputable place to purchase a replacement battery for a Mac notebook? Obviously, cost is a consideration too. He'd rather not pay $129 directly from Apple for their branded battery if he doesn't have to. And is there a compatible brand that is consistently better than the others? The MBP model he got is MA610LL, but it's been upgraded to 4GB of RAM and a 500GB hard drive.