Both battery packs measured about 1.4V, yikes! I was able to revive one of the two batteries - a Type I - by rigging up my RC airplane charger and doing a constant current charge at 400mA. This involved some bare wires propped up against the battery's terminals with a heavy book. I put about 200 mAh into the battery, after which its voltage had risen to about 14.5V. The battery was then recognized in the Duo when I had it in the dock, so that charged it some more until it said it was full. The "full" battery only powered the Duo 230 for about 15 minutes, but at least it worked.

I'm trying the same trick on the second battery - a Type III - but so far not as much success. I put 250 mAh into the battery, which took its voltage up to about 11V. But when I put the battery into the Duo in the dock, it showed the icon of a battery with an X. Now I'm charging it further on my RC airplane charger to see if I get a better result if I charge to a higher voltage. It's at 12.33V and climbing now...