The $64,000 question is what kind of PowerBook battery are we talking about.

The reason I ask is because 5300 batteries are NiCad, whereas newer batteries (I.E. iBooks / 233mhz PB's +) are Lithium Ion. If you just find any charger and wire it to have the same points, there could be some issues with over/undercharging the battery because of current control and regulation. If you have a newer PB you may need to wire one youself, but if it's an older one nearer to the G3 PB reign, you maybe able to make a couple changes since it's should be in about the same family.
MacBook 2GHz Intel Core 2 Duo w/ 2GB DDR2 RAM & 120GB SATA 5400RPM HDD
Canon Rebel XTI
Google Cr-48 Beta Laptop