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

From: Dwight K. Elvey <dwight.elvey_at_amd.com>
Date: Fri Oct 22 12:07:06 2004

Hi Tom
>From: "Tom Peters" <tpeters_at_mixcom.com>
>
---snip---
>2. NiCD batteries never had a memory effect either! Read the literature
---snip a lot of good stuff---

 Thank you for mentioning this. I think, a lot of what people
think of as memory is caused by unequal charging of battery
stacks. As the cell that has the most charge remaining reaches
full charge, the current through this cell reduces. The cell
that has been lagging behind, never receives a full change.
Flattening the stack lets them all start from a more equal
playing field.
 The problem people miss with flattening is that if a cell
is reverse charged, the depolarizers are at the wrong ends
of the cells and the gas pressure builds up causing the burst
seal to fail. Although, immediately after charging, this cell
seems to work fine, within a month or so the cell will fail,
simply because it dries out inside :( It may also leak on
things.
 As I stated before, long term storage of NiCads is best done
with them fully discharged. This keeps metal fingers from
developing that cause the shorted cells that we often see.
One can also store them at full charge because this tends
to blow out any metal fingers that grow. The problem is
that storing mostly discharged cell is the worst since there
is both the voltage that causes the metal fingers to grow
and not enough capacity to blow them out when they do short.
Dwight
Received on Fri Oct 22 2004 - 12:07:06 BST