When using NICad or NIMH battery's do not go below 0.85V per Cell or you will distroy them.
In general 0.9 V per cell will do, so for a 6Cell pack this is 0.9Vx6=5.4V.
If you use higher voltage settings like 1V per cell this will not make them compleet emty and you can get memory effects with the NICAD's.
Greatz Whacky.