The term ‘memory effect’ may sound like a problem of the nervous system to many but regular used of rechargeable batteries may know what we are referring to. It is a common problem that afflicts nickel-cadmium and the nickel–metal hydride rechargeable batteries. Only the most advanced cell chemistry– the Lithium Ion and the Lithium-Ion polymer cells are completely free of memory effect.

The worst hit of all rechargeable batteries is of course, the nickel cadmium battery. The Nickel Metal Hydride or Ni-MH rechargeable batteries hold up much better to the memory effect and this counts as one of its biggest advantages when compared to the NiCad batteries. That coupled with the fact that the Ni-MH battery is non toxic unlike the NiCad which is an environmental risk with Cadmium toxicity makes Ni-MH more popular. But for now, let’s examine and understand what the term ‘Memory effect’ means.

Memory effect is a layman term used in place of the more accurate – “Voltage Depression”. It is also called the ‘lazy battery effect’ and causes the battery to hold less charge. Memory effect is believed to take place when a rechargeable battery is charged without first completely discharging it. The battery remembers the level from where it was ‘topped up’ and doesn’t charge to its full capacity. When the battery with a memory effect is used it discharges much more quickly than it should because now it is recognizing the shortened cycle!

Voltage depression means that the peak of the battery drops more quickly than normal even though the total energy remains almost the same. This to the average user may look like the battery is not holding its full charge, which seems similar to memory effect. A common problem with high load devices like two way radios and barcode scanners, voltage depression is caused by repeated overcharging of a battery that results in the formation of small crystals of electrolyte on the plates. These crystals suffocate the plates, increasing resistance and lowering the voltage of some individual cells in the battery. With the result those individual cells discharge quicker than the other cells and the voltage of the battery as a whole plummets. Voltage depression is actually a charging problem – the seeming memory effect can occur with overcharging, under-charging and even exposure to battery-inappropriate temperatures.

Although memory effect can be seen heavily in NiCad batteries and to some extent in Ni-MH batteries, the Li-Ion battery is totally safe from this phenomenon. However, you would still find some users who associate memory effect with all rechargeable batteries. But as we can see one cannot generalize this problem to all battery packs.

Even in NiCad and Ni-MH batteries the memory effect can be fixed to some extent. Here are a few ways that can help you maximize your rechargeable batteries’ life and get the most out of them:

- Memory effect is more often than not a charging fault and modern trickle chargers usually precipitate this problem. So in the best interest of your batteries, invest in a good quality charger. Another point to be noted on the subject of chargers is to never charge a Ni-MH battery in a NiCad charger unless you know for sure that the charger supports both chemistries. Certain chargers are universal battery chargers also known as tri-chemistry battery chargers. These battery chargers are able to charge all three chemistries - NiCD, NiMH and Li-Ion.
- With NiCad batteries, often it helps to occasionally discharging them completely before charging them again. You don’t have to discharge them completely – less than 1v per cell for NiCad and NI-MH would be good enough.
- Ensure proper storage of the batteries because external conditions like temperature are often the silent culprit of memory effect. Don’t leave them exposed to high heat or in a place of high humidity. If you want to store them by refrigeration, seal them well in a bag and add in a pack of silica gel to keep moisture at bay.

Rechargeable batteries provide an excellent alternative to disposable batteries and can save a lot of money for you. Don’t let something so avoidable (or correctable!) as memory effect steer you away from them. Try these tips and you can increase the life of your battery and maximize its performance.