Myths/Common Misperceptions - Memory Effect

Use it or lose it

Urban legend buffs take note:  Although the so-called "memory effect"- also known as the "lazy battery effect"-inspires a great deal of superstitious and obsessive behavior in its adherents, actual instances of the phenomenon have been nearly impossible to create under controlled lab circumstances.

In fact, the most common example of a true memory effect in batteries is found in the behavior of rechargeable cells in outdated, expensive, unmanned electronics aboard satellites in orbit above the earth.  Still, some people firmly believe that recharging a battery before it has drained completely damages the battery.

Scientists refer to the more down-to-earth problems of rechargeable battery performance in the kinds of batteries most people commonly use (such as those in digital cameras, PDAs, MP3 players, and laptops) as voltage depression.  Voltage depression happens when batteries are incorrectly charged, due to human or mechanical error.  Continual overcharging of a battery can cause electrolyte crystals to form inside the battery, clogging its plates.  This causes increased resistance and, in some cases, a reduction in the voltage in some individual cells in the battery.

The three most common chemical types in consumer electronic devices are NiCad batteries (Nickel Cadmium), NiMH batteries (Nickel Metal Hydride) and, Li-Ion batteries (Lithium Ion).  Voltage depression occurs primarily in NiCad batteries. NiMH batteries rarely experience this type of deleterious effect.  Li-Ion batteries are NEVER affected.  Devices with internal, rechargeable batteries increasingly use Li-Ion batteries, eliminating any concern over reduced battery capacity due to a variation in charging cycles.

If a battery fails to hold an adequate charge or experiences some other form of voltage depression, a more likely culprit would be inadequate charging, overcharging, damage from storage in extreme cold, or exposure to high temperatures.

A battery could hold less energy as it aged, but this would be more a function of time than a consequence of whether or not a user fully depleted the battery at each use.  Most manufacturers sell the rechargeable batteries that accompany their devices (such as notebooks and digital cameras) as separate, replaceable units to increase the useable life of the product.

Power tips

Whether bundled with an electronic device or sold separately, rechargeable batteries vastly outperform traditional alkaline batteries in high drain electronic devices.  Ecologically sensitive, convenient, and economical, the life and usefulness of these batteries can be significantly enhanced in a few easy ways.

A good charger lengthens the life of batteries. NiMH batteries should never be charged in a NiCad charger, unless the charger specifically accommodates both types of batteries.  Chargers with micro-controller chips fine-tune the flow of current to each battery to assure optimal performance.  Some chargers condition (or fully drain and refill) batteries after a charge, ensuring optimum lifespan.

A battery needs to be fully charged before its initial use.

NiCad batteries should be discharged fully periodically.

Batteries should be stored in a cool, dry place. Extreme heat (such as the interior of a car) damages rechargeable batteries.  Keeping batteries in the refrigerator can expose them to undesirable moisture, so an absorbent silica gel pack should be used.

More information on batteries