NiCD, NiMH, & Memory Effect

What is the difference between Nickel Cadmium (NiCad) and Nickel Metal Hydride (NIMH) batteries? What is “Memory Effect?”

Both NiCad and NiMH batteries are rechargeable. The main difference between the two is the fact that NIMH batteries offer higher energy densities than NiCads. In other words, pound for pound, NIMH delivers approximately 30% more capacity than its NiCad counterpart. What this translates into is increased runtime from the battery with no additional bulk. NIMH also offers another major advantage: NiCad batteries tend to suffer from what is called a “memory effect”. What this means is that when a NiCad battery is only partially discharged before charging, the battery “forgets” that it has the capacity to further discharge all the way down.

To illustrate: If you, on a regular basis, fully charge your battery and then use only 40% of its capacity before the next recharge, eventually the battery will become unaware of its extra 60% capacity which has remained unused. Your battery will remain functional, but only at 40% of its original capacity.

The way to avoid the dreaded “memory effect” is to fully cycle your NiCad battery at least once a month. In other words, fully discharge your battery and then fully charge it.

Batteries can be discharged by allowing the device to run on the battery until it ceases to function. This will insure your battery remains healthy. NIMH batteries are “memory free” – they do not suffer from this affliction. Thus, if you have a NIMH battery, the only time it is necessary to cycle it is during its initial use and after a long storage period. This is done to “exercise” the battery and bring it up to full capacity.