Battery Q&A: Memory Effect & Voltage Depression

[mister_okay]

Hello everyone:)

I have questions regarding the "memory effect" and voltage depression.
1.) Could someone explain to me in layman's terms exactly what they are? I don't quite understand the explanation on wikipedia.org.

2.) Additionally, my friend told me that when you turn your mp3 player off (samsung YEPP) you should take out the battery because even with the power off, it will drain. Is this true?

 

[chroot]

1) The memory effect is usually attributed to non-uniform plating of the electrodes inside the battery.

2) Your battery will actually drain even if it's not in the player. It is possible that your player will cause it to drain a bit faster, however, depending upon how it is built (is the power switch mechanical, or electrical?) Some electronics constantly consume small amounts of power. If you really want to know, hook a sensitive ammeter in and see how much current it draws when powered off.

- Warren

 

[mister_okay]

But what exactly is the memory effect and voltage depression?

 

[Cliff_J]

Mister - one is a specific problem and the other is mistakenly labeled as the same. Since you've read the description and likely aren't building a satellite it doesn't really matter if you're using a widely accepted term (even if technically slightly off).

The battery normally offers a certain voltage, let's say 1.2V per cell. Now when fully charged and unloaded this may be 1.3V. When being used at high loads it may be 1.1V and falling as it drains. If the battery is suffering from being abused, it will read much lower, like 1.0V when you try to use it. A new battery fully charged wouldn't read 1.0V until it was say less than half full, so the equipment could mistake this for a battery that is much less full than it actually is.

This is more of a problem with rechargable batteries because an alkaline battery is generally 1.5V and the rechargable is 1.2V, thus meaning the equipment would need to be designed to work this way (and usually is). But when it comes to figuring out how much charge is left in the battery, its an educated guess and can be wrong. Having batteries that can be slowly damaged and change their behavior increases the likelyhood the guess will be more wrong.