DN-1 and MN-1 replacement batteries
The NiCd DN-1 batteries for the DS-1, DS-2 and DS-12 servo units and the MN-1 batteries for the MB-1 are over 20 years old and they won't hold charge for long, if at all. I have brand new DN-1 replacement NiMH batteries that can be recharged over 500 times. These batteries have 20% higher capacity than the original NiCd betteries (330mAh instead of 280 mAh), and without the dreaded memory effect. These NiMH batteries are FULLY compatible with the DH-1 (it is untrue that the NiMH batteries would damage the DH-1). Also they have better performance and provide twice as many recharging cycles than the NiCd batteries. Furthermore, they do not contain highly toxic cadmium, making them the most environmental batteries available today.

The price is $25 for each DN-1 replacement battery, plus $7 postage. Two DN-1 replacement batteries are needed to recell each MN-1. I also have recelled MN-1s at $140 a pair.
DN-1 and MN-1 replacement batteries