The myth of the memory effect- was: NMIH batteries - was: Re: HP 25 and HP55

From: Dave Dunfield <>
Date: Fri Oct 22 05:40:38 2004

Thanks for the info on NMIH.

>2. NiCD batteries never had a memory effect either!

I knew this would spark a thread on the existance or non-existance of memroy
effect - I think they are a lot better now than they were (as are chargers),
however Nicads (especially older ones) which regularily discharged only partly
do lose capacity - I have observed it.

>I think what can happen is that some cells discharge a lot sooner than
>others, since in the real world the internal R is lower for some cells than
>others. Since you are now pulling current *backwards* through at least one
>cell in the stack, odd are good that some day one of the cells is going to
>reverse on you, and become a highly inefficient inverted battery, one
>that's unlikely to ever take an appreciable charge again. This is a
>real-world problem for discharge devices that don't have both a timer and a
>voltage monitor, and some ever sense temperature too.

Yup - best way to kill a nicad "pack" is to fully discharge it - that is why
I use individual cells, and discharge them in parallel through a diode - no
cell ever goes below .7v.

>Here's a battery maker saying No Memory Effect in currently produced product.

Ah - the catch phrase is "currently produced" - As I indicated above, I think
things have improved... but the Nicad cells I am using are 10+ years old.

I can provide references to manufacturers telling you to be sure and fully
discharge your cells from time to time as well ... it's a question that is
still being debated, and nobody is going to convince anyone else either
way - my personal experience is that calls which are carefully charged,
and just a carefully full-discharged retain their capacity and last a lot
longer than cells which are not fully discharged... Agreed thad modern NMIH
cells do not seem nearly as "sensitive". YMMV.

But ... we drift OT ... thanks for you input.

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools:
com             Vintage computing equipment collector.
Received on Fri Oct 22 2004 - 05:40:38 BST

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