Depending on your HPC, this should not be a problem. They have many good features, and last a long time. You will find them considerably more expensive than Lithium or Alkalines. Their starting voltage is 1.25v and they hold their charge for the life of the battery. They are very good at responding to power surges, which means they provide reliable power for many applications.
NiCads have several disadvantages.
It's use it or lose it with NiCads. Also, to get full potential from the batteries you have to let them drain completely. As the crystals build up, the battery's maximum charge potential degrades. Finally, if you are environmentally conscious, NiCads contain heavy metal cadmium, which is a targeted environmental pollutant. Designers find NiMH attractive because its energy density is considerably greater than NiCad.