The original battery of my iBook holds no juice at all, so I'd like to purchase a replacement. Mine says "A1080, 14.4V, 5200mAh." However, all of the A1080 batteries that I see on line say 4400mAh!! Are we supposed to replace 5200mAh battery with 4400mAh one? What effect does this have? Or is my iBook totally outdated and cannot get a replacement battery? Thank you for your help!