The Apple iBook G4 15-INCH SERIES Battery is a battery designed for the iBook. It stores energy for use when you’re not near a power outlet or don't have your power cord handy. In terms of storing and subsequently releasing energy, this battery is fantastic. So far, it works just like the original battery I had with the device, so I get about 4.5 hours per charge if you're not running a million applications and using the airport (two activities that will drain the battery quickly).