Memory effect, known as battery effect, lazy battery effect, or battery memory, is a term commonly used in the battery industry, and it dates back to battery technologies such as Nickel-cadmium and Nickel-metal hydride. The battery memory effect is a reduction in the longevity of a rechargeable battery’s charge, due to incomplete discharge in previous uses. It is a common scenario when the battery frequently operates at partial state-of-charge (PSoC). The memory effect would mean that the battery tends to remember this regular usage pattern of low depth-of discharge (DoD) and gradually loses its ability to deliver energy equal to its usable capacity due to a lower window of working voltage.
Some types of batteries, such as nickel-cadmium and nickel-metal hydride, can develop a memory effect when only partially discharged before recharging. This “memory” reduces the capacity of subsequent charges and thus future battery life in a given device. The effect can also be caused by poorly-designed chargers. Newer types of batteries, such as those based on lithium ion and lithium polymer, offer better capacity and an improved ability to hold a charge while not in use, while also not demonstrating a memory effect when partially discharged.
The memory effect can be mitigated by diligent battery use: fully discharging and recharging. One can recondition batteries with a memory effect by deep discharge and charge cycles. Some chargers have specific battery reconditioning modes as well.
In general, most people with a decent charger don’t have to worry about memory effect any longer. Only consistent partial charges tend to produce the effect. In fact, draining the capacity completely is worse for the cells’ overall longevity and only advisable by those seeking maximum voltage for purposes such as remote control operations.