Whatever you do, do NOT put cells from ANY iBook battery into the PowerBook 150 battery. An iBook battery, like just about all laptop batteries made in the last 10 years, uses Lithium-Ion (Li-Ion) cells. The PowerBook 100 series batteries (apart from the 190, which is Nickel Metal Hydride (NiMH)), are ALL Ni-Cad (Nickel Cadmium) based. If you mix NiCad with Li-Ion, the results may be rather....dangerous.

You might want to ask in the 68k PowerBook forum...but whatever you do, make sure that whatever cells you buy are definitely Ni-Cad cells. Never, ever mix different types of cells when recelling laptop batteries.