DN-1 replacement battery
The NiCd DN-1 batteries for the DS-1, DS-2 and DS-12 servo units are over 20 years old and 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 $23 for each DN-1 replacement battery, plus $7 postage.
Left one is the original Nicad DN-1,
Right one is the NiMH DN-1 replacement.
The voltage is 3.6V, and the capacity is 330mAH.