Technically, NiMH batteries do not have a memory effect. However NiMH batteries can experience voltage depletion, also called voltage depression, similar to that of NiCd batteries, but the effect is normally less noticeable.

To completely eliminate the possibility of NiMH batteries suffering any voltage depletion effect manufacturers recommend an OCCASIONAL, complete discharge of NiMH batteries followed by a full recharge. NiMH batteries can also be damaged by overcharge and improper storage.

Most users of NiMH batteries don't have to be concerned with this voltage depletion effect.

But if you use a device say a flashlight, radio, or digital camera for only a short time every day and then charge the batteries every night, you will need to let the NiMH batteries run down occasionally.