The Dreaded Memory Effect

What is the dreaded memory effect? Simply put, it's a condition that is particular to NiCad batteries where the battery can never be recharged to its maximum usable voltage again. Here is what usually causes the dreaded memory effect:

When a NiCad battery has been fully charged and then begins to discharge due to normal use, a strange thing happens (chemically, inside the battery) if the battery is repeatedly recharged before it is fully discharged. This strange thing is called the "dreaded memory effect", since the battery will "remember" the voltage it was at when the recharge begins to take place and will never go much higher than that voltage ever again.

For example, if you took a normal 9 V NiCad battery, fully charged it to 9 volts, then put it in a circuit, like the Board of Education, and allowed it to discharge to, say 6 volts, then took it out and began to recharge it again, and did this repeatedly, the battery would eventually never charge up over 6 volts again. Other practical examples of the NiCad battery memory effect occur in household appliances like a mini hand vacuum or portable hand drill. If these appliances are repeatedly recharged without draining their batteries completely, they may never work as they did when they were new. How many "dead" battery-operated appliances do you have laying around the house that will never see another moment of useful application? Their useless working condition is probably due to the memory effect we're discussing here. In other words, their NiCad batteries were recharged too often and before they were fully discharged.

In order to prevent the memory effect, a NiCad battery needs to be both fully charged and then nearly fully discharged to get the maximum life out of it. Otherwise, the battery will revert to a lesser maximum voltage on subsequent charges. There is much controversy regarding the memory effects of NiCad batteries; some experts say it exists while others say it doesn't, so it all depends on what battery expert you speak with or read about. Nevertheless, your author has experienced this memory effect for years, now, so it does appear to be real. That said, with newer battery technologies coming on the market coupled with newer designs of NiCad batteries themselves, this once daunting "dreaded memory effect" will go away and hopefully be "forgotten forever".

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