Memory effect

Memory effect, also known as lazy battery effect

Affects nickel cadmium rechargeable batteries almost exclusively. Some sources say that nickel metal hydride batteries are also affected, to a much lesser degree.

NiCd batteries suffer from this effect when they are often recharged before they have been fully discharged; subsequent use will not get as much power out of the battery. NiCd rechargers will sometimes include the ability to fully discharge batteries before beginning recharging as a result. Never, however, discharge rechargeable batteries to zero voltage.

Lazy battery effect is caused by crystalization within the battery's electrolyte, reducing the available capacity. Much of the lost capacity can be recovered by a few deep discharge cycles. Some more modern rechargers claim to be able to break the crystalization by pulse charging.