Batteryspace.com sells NiMH tabbed 4/3AF cells. Getting eight of them to fit into that tight PB1400 case may be a problem, so the tab soldering must be done in a very compact manner. NiMH batteries are relatively safe to work on so the PB 1400 battery is a good place to start learning about recelling.

The iBook battery cells are lithium ion technology, the kind that overheats and explodes if abused. Best to avoid recelling lithium batteries unless you acquire the instrumentation and knowhow to meet all safety requirements.

Your lithium cells are not appropriate for use in the PB 1400: different voltages, different charger, different safety circuits.