Memory effect on NiCd, NiMH, and Other Battery Types
What is memory effect?
Memory effect is the decrease of charge capacity of batteries because of improper use. The memory effect is most prominent in nickel cadmium (NiCd) batteries. Nickel cadmium (NiCd) need to be completely discharged before being recharged. If these batteries are recharged while they still have 40% of their charge, this 40% is lost so that the batteries will now have 60% left. The successor to the Nickel cadmium (NiCd) – the Nickel Metal-Hydride (NiMH), is less susceptible to the memory effect. It is only affected by a small degree but proper care is still essential to prolong the life of the battery.
The term memory effect is derived from the idea that batteries “remember” the remaining charge and lose it permanently when charged. The term offers a close idea to what really happens what we call voltage depression.
What is voltage depression?
From the word itself, voltage depression causes a decrease on the output voltage of batteries. This happens when Nickel based batteries are overcharged. The overcharging of batteries causes crystal formation on the nickel plate inside the batteries. These crystals cause small “short circuits” inside the battery and effectively reduce its voltage – not the charge capacity.
So we can charge Nickel based batteries without fully discharging them?
Yes. You can do that even on Nickel Cadmium batteries (NiCd) which are well known for this problem. Unfortunately, majority of the battery chargers available determine the charging time by a count-down timer. A count-down timer based charger cause overcharging on not completely discharged batteries – and we get the “memory effect.” The kind of battery charger you need is a smart charger. This type of charger has microprocessors in them that determine when the battery is fully charged. Once the battery reaches a specific voltage and temperature, the charger stops charging. This protects the battery from overcharging.
Is there any way to fix a battery that has suffered from memory effect?
To some extent – yes. If a battery seems to suffer from memory effect or voltage depression what you need to do is cycle charge the battery. Cycle charging means that you need to discharge the battery completely then recharge it completely. This doing this can vaporize the crystals on the nickel plate.
For severely affected batteries, performing a cycle charge will have minimal effects. This is because the crystals on the nickel plate have become so large that they have already damaged the plate itself. The best thing you can do is buy a new set of batteries.
Would you rather "save" a dying battery or buy a new one?
What about Lithium-ion batteries?
Lithium-ion (Li-ion) batteries do not suffer from voltage depression, unlike nickel cadmium batteries, due to crystals since they don’t have a nickel plate. They suffer from memory effect after being recharged a number of times. There is a limit to as to how much you can recharge them before they begin to degrade very fast.
They can also suffer from memory effect when some gasses inside the battery cell escapes. This can happen when it overheats or is punctured. The gasses have electrodes that form a part of the overall charge of the battery.
For Nickel Cadmium (NiCd) or even Nickel Metal-hydride (Ni-MH), always discharge before recharging and avoid partial charging. Discharge them completely when you don’t plan to use them soon.
For Lithium-ion (Li-ion) batteries, the less you charge them, the longer they will last. It means that when you have a laptop and you are near an outlet - use the AC adapter instead of the battery. For cell phones, do not use the unit while charging. This is a well known cause of memory effect on cellular batteries.