NiMH batteries do not have a "memory effect". However NiMH batteries can experience what is known as "voltage depression", similar to NiCd batteries, but the effect is generally less noticeable. To eliminate the possibility of NiMH batteries suffering voltage depression 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 depression effect, but if you use a device for only a short period of time every day, and then charge the batteries every night, you will need to let the NiMH batteries run down occasionally to keep this effect from occurring.