Apple has released new software that helps the batteries in 15-inch PowerBooks perform better.
The 400k update, "Aluminum PowerBook (15-inch) Battery Update v1.1", is available for download from Apple's website.
If your PowerBook can use this update, it will also be available through Software Update.
Notes accompanying the software reveal: "This update aids the 15-inch Aluminum PowerBook battery in performing at full capacity."
More detailed Apple notes reveal: "This firmware update is required to keep your battery life up to specification, may recover battery life in some batteries that have developed short run times, and in some cases can recover batteries that are not recognized by the system."