Unc Cece had it “half-right” on his Ni-Cad Battery answer recently published.
I used to manage a two-way radio shop. Now, as you can imagine, Ni-Cad batteries were very popular for the handheld radios, as you could simply recharge them instead of having to buy dry-cell or alkaline batteries. One of our biggest problems was “ni-cad memory.”
It would occur when a user would take his radio out of the charger, use it for 15-20 minutes or so, then put it back in the charger. Pretty soon the battery would have only 15-20 minutes of useful life left in it. I saw this happen more than once.
While I can not give you the “scientific” answer why this occurs, I can tell you it happens, and quite a bit. I had a Ni-Cad battery on a amatuer radio of mine, and with proper charge-discharge cycles, the battery lasted me 6 years! Not bad for a product that is designed to last 1 1/2 to 2 years!
There is one way of eliminating “memory effect” from Ni-Cad cells, and that is deliberate “overshock”, as we called it - the application of high voltage for a VERY short period of time, say 2 seconds or so. CAUTION!!! Do NOT try this unless you have a variable power supply, and TWO DVMs, one to monitor the power supply, the other the battery! This can result in explosion of the battery pack if the surge voltage is left on the pack too long!
Cece, you’re right in stating the voltage in the battery is still there underneath the “memory effect”, but aside from having a TRAINED TECHNICIAN perform the above on the battery pack, there is no way to access that stored votage underneath the memory effect.
There was a VERY informative article on Ni-Cad and Ni-MH (Nickel-Metal-Hydride) batteries in a recent issue of QST magazine, I invite you to visit the ARRL website at ww.arrl.org and do a search for Ni-Cad for the article. It explains the memory effect much better than I ever could.
Thanks and keep up the good work of informing the “unwashed masses”!
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