Looking at replacement batteries:

http://www.batterycountry.com/ShopSite/powerbookduo_laptop.htm

they're listed as 12V 1100mAH, so if there's 10 cells in them, my guess would be that they were 1.2V cells (which is a standard AA NiMH), if that helps any. But I'd wait and see if someone else who knows for sure can chime in.

I have a powerbook 230 as well, so I'd be interested to hear how this works out for you.