NiCad's are very finicky. The only thing they are good for is very high discharge current (similar to the cold cranking amps rating in car battery). Other than that they don't have nearly as much capacity as NiMH, high self discharge rate, memory and usually goes bad in a few years the most. So in your case if you want to run your MD at high speed then rebuild the batteries with new NiMH cells. Otherwise use AA alkalines which are much more reliable but the MD-2 won't run at top speed with AA and does require the MN-2 to run at top speed.
Originally Posted by BradleyK