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The Nickel Cadmium memory effect – fact or fiction?
Last Edited September 13, 2019 | Author BatteryGuy |
Category Battery FAQs, Nickel Batteries
There are a few hot potatoes in the battery
world and memory effect in NiCad
Cadmium batteries is one of them. The
story goes that if you discharge a Nickel
Cadmium battery to exactly the same point
thousands of times and then recharge it,
the battery will remember this discharged
point. As a result, if you then discharge the
battery to the moment when it expects
recharging to start, but instead of
recharging you continue to discharge, the
voltage will suddenly drop.
How the rumor started
This idea did not come out of nowhere.
NiCad batteries were used in satellites
during the 1960s where their lives would
follow a very exact pattern – recharging for

Contents
1. How the
rumor
started
2. Finding a
real memory
effect
3. The
unshakable
myth
4. Further
reading:
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12 hours via solar
panels and then
discharging for 12
hours. The
discharge and
recharge patterns
would be virtually
The memory affect was first
identical every
discovered in batteries used
day and they
on satellites.
would repeat this
thousands of
times as they orbited the earth.
Pensabene and Gould, two scientists
working at GE, studied these batteries after
they had been in use and noticed the
voltage drop when they were discharged
below the point when recharging would
have normally started. In 1976 they
published a paper called “Unwanted
Memory Spooks Nickel Cadmium Cells”
outlining their findings.
From there the myth took hold and almost
any NiCad issue suddenly got blamed
on memory effect.
Finding a real memory effect
Widely ignored is that Pensabene and
Gould also attempted to repeat the memory
effect in the laboratory by subjecting NiCad
cells to over 5,000 cycles of identical
charge and discharge cycles but failed to
see the same result that they had observed
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in used satellite batteries. A similar attempt
in 1996 by scientists Sato, Arakawa and
Kobayakawa also could not produce cells
that exhibited the memory effect.
Despite this, many people still pointed to
the memory effect as a shortcoming of
Nickel Cadmium. General Electric
attempted to correct this in a technical
notice where they pointed out that in order
to even have a remote chance of the
memory effect occurring, three steps were
required:
1. The battery must be discharged to
exactly 25% (+/- 1%) of its capacity
2. The battery must then be recharged to
exactly 100% and then the recharging
must be cut off.
3. This pattern must be repeated
hundreds of times.
It is clear that there are very few real world
applications, perhaps none, where such a
situation would occur. Users of battery
powered devices never discharge to exactly
25% hundreds of times and it is also
common place for batteries to be
overcharged (left charging even after they
have reached 100%). This latter practice is
even thought to clear any memory effects
anyway.
General Electric, who for all intensive
purposes started the rumor, has also stated
Battery
Categories
4
“the idea of a memory phenomenon in
nickel-cadmium batteries has been widely
misused and understood …[and]… has
become a catch-all ‘buzzword’ that is used
to describe a raft of application problems”.
The unshakable myth
Despite all that has been done to show the
memory effect is not a real world issue,
misinformation abounds. The Compact
American Dictionary of Computer Words
describes memory effect as “A property of
NiCad Batteries in which the amount of
charging they accept at one time fixes the
maximum amount of charging they can
accept in subsequent recharges”
Even a 2013 research paper looking at the
memory effect in Lithium-Ion batteries
starts with “Memory effects are well known
to users of nickel–cadmium and nickel–
metal-hydride batteries.”
In short, memory effect in all likelihood does
not exist and even if it did, it occurs under
such specific circumstances that the
chances of it happening in any particular
application are almost zero, if not zero.
It’s also worth noting that stories of the
memory effect are not limited to NiCad. In
2013 Petr Novak at the Paul Sherrer
Institute, working alongside Toyota
Research Laboratories, claimed to have
found a similar phenomenon in Lithium-Ion
batteries . This has yet to be confirmed by
other researchers.
Further reading:
http://www.battcon.com/papersfinal200
3/mcdowallpaperfinal2003.pdf
https://en.wikipedia.org/wiki/Memory_ef
fect – Wikipedia on the memory effect
http://phys.org/news/2013-04-memoryeffect-lithium-ion-batteries.html –
initial findings of a possible memory
effect in lithium-ion batteries
http://www.resrchintl.com/memory_effe
cts.html – Research International on
the memory effect
http://www.z80.info/nicd2.txt – Ken A.
Nishimura’s 1995 paper ‘Some
Ramblings About NiCd Batteries’
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