BU-807: How to Restore Nickel-based Batteries

Discover if memory is myth or fact, and how to prevent and eliminate it.

During the nickel-cadmium years of the 1970s and 1980s, battery ills were blamed on “memory.” Today, the word memory is still being used to advertise newer batteries as being “memory-free.” Memory comes from “cyclic memory,” meaning that a nickel-cadmium battery could remember how much energy was drawn on previous discharges and it would deliver the same amount on repeat discharges. If more was demanded, the voltage would abruptly drop as if to protest against imposed overtime.

Memory occurs when keeping a NiCd battery is overcharged. The effect can be reversed with a pulse charge, but it is more effectively to apply a full discharge cycle. Figure 8-26 illustrates the anode of a normal NiCd, memory that formed, and a restored anode.

New nickel-cadmium cell.The anode (negative electrode) is in fresh condition. Hexagonal cadmium-hydroxide crystals are about 1 micron in cross section, exposing large surface area to the electrolyte for maximum performance.


Cell with crystalline formation. Crystals have
grown to 50 -100 microns in cross section, concealing large portions of the active material from the electrolyte. Jagged edges and sharp corners can pierce the separator, leading to increased self-discharge or electrical short.


Restored cell. After a pulsed charge, the crystals are reduced to 3–5 microns: an almost 100% restoration. Exercise or recondition is needed if the pulse charge alone is not effective.

Figure 1: Crystalline formation on nickel-cadmium cell. Crystalline formation occurs over a few months if a battery is overcharged and not maintained with periodic deep discharges.

The modern nickel-cadmium battery no longer has cyclic memory, but it suffers from crystalline formation. The active cadmium material is applied on the negative plate and with time, a crystalline formation develops that reduces the surface area and lowers the battery performance. In advanced stages, the sharp edges of the forming crystals can penetrate the separator, causing high self-discharge that can lead to an electrical short.

When introduced in the early 1990s, nickel-metal-hydride (NiMH) was hailed as being memory-free, but this claim is only partially true. NiMH is subject to memory but to a lesser degree than NiCd. While NiMH has only the nickel plate to worry about, NiCd also includes the memory-prone cadmium negative electrode. This is a simple explanation of why NiMH is less susceptible to memory than NiCd.

Crystalline formation occurs if a nickel-based battery is left in the charger for days or repeatedly recharged without a periodic full discharge. Since most applications fall into this user pattern, NiCd requires a periodic discharge to 1 volt per cell to prolong service life. A discharge/charge cycle as part of maintenance, known as exercise, should be done every 1–3 months. Avoid over-exercising as this wears down the battery unnecessarily.

If regular exercise is omitted for 6 months or longer, the crystals ingrain themselves and a full restoration with a discharge to 1 volt per cell may no longer be sufficient. Restoration is often possible by applying a secondary discharge called recondition. Recondition is a slow discharge that drains the battery to about 0.4V/cell and lower.

Tests by the US Army indicate that a NiCd cell needs to be discharged to at least 0.6V to effectively break up the more resistant crystalline formations. During this corrective discharge, the current must be kept low to minimize cell reversal as NiCd can only tolerate a small amount of cell reversal. (See BU-501: Basics About Discharging). ). Figure 2 illustrates the battery voltage during a discharge to 1V/cell, followed by the secondary discharge to 0.4V/cell.

Exercise and recondition features of a Cadex battery analyzer

Figure 2: Exercise and recondition cycles of a battery analyzer (Cadex).

Recondition restores NiCd batteries with hard-to-remove memory. Recondition is a slow, deep discharge to 0.4V/cell.

Courtesy of Cadex

Recondition is most effective in rejuvenating batteries that have not been exercised. Battery analyzers (Cadex) automatically apply the recondition cycle if the user-set target capacity cannot be reached with a discharge to 1V/cell alone. Although low performing batteries can often be fully restored, high self-discharge makes some old-timers unusable for service.

Most ship batteries in large aircraft are NiCd. Resembling an oversized starter battery in a vehicle, these batteries are serviced by applying a full discharge and keeping each cell at zero volts for 24 hours before recharge. Each cell is then checked for correct voltage, and capacity verification is taken with a full discharge/charge cycle before installing them again in the airplane. Aviation batteries follow strict maintenance schedules.



As battery care-giver, you have choices in how to prolong battery life. Each battery system has unique needs in terms of charging, depth of discharge and loading that should be observed. The following two papers summarize what batteries like and dislike.

BU-415: How to Charge and When to Charge?
BU-706: Summary of Do’s and Don’ts


Last updated 2018-05-10

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Comments (51)

On December 6, 2011 at 11:43am
COburner wrote:

I’ve tried the deep reconditioning method advised here on some individual NiCd and some multicell tool battery packs. I’m unsure if you could deep discharge multicell packs effectively without taking the pack apart and discharging each cell individually—so far that’s what I’ve done because used cells vary so much in capacity. If you try to discharge the whole pack (even very slowly) it seems some will hold charge a long time while others go into reversal. I’m not sure if that harms the weaker cells or not. If you need to discharge each cell individually it becomes an enormous hassle to keep a pack conditioned. Any advice on this?

I’m also quite unclear from this article if the target for deep conditioning discharge of 0.4 v. is a no-load voltage or what? I’ve assumed it’s a no-load voltage, but it takes a very long time to get there at low disch rate. The battery that’s 0.4 v under 50 ma. load will repeatedly bounce back to 1.1 v. under no load. Can you clarify this?

On July 28, 2012 at 12:57am
Graham Jones wrote:

I have the same experience as COburner, and would greatly appreciate your advice. Many thanks

On July 29, 2012 at 8:50am
robert wrote:

What current should be used for deep discharge? example 0.1 C or lower?

On August 4, 2012 at 4:56am
Arek wrote:


Works with batteries ni-cd for 18 years. Much of that time I gave discharge ensure preservation. Max. discharge current for a typical AA cell is 15 mA, the High Current SC - 50mA. The current is independent of the capacity of the cell, since less capacious cells are resistant to reverse polarity.
Sorry for the english, I come from Polish.

On August 4, 2012 at 2:49pm
COburner wrote:

Agree with Mr. Arak. Slow discharge seems best for reconditioning purposes. For typical used AA NiCd of 1000 maH capacity (C), C/50 = 20 ma. For typical sub-C of 2000 maH capacity, C/50 =40 ma. One might argue that anything slower than C/20 is OK, but I’m not sure of that.

I certainly wish the scientist/engineer who wrote the article, or others at his company, would respond here. Since posting the question 7 months ago, I’ve continued to experiment. First, I think I was wrong in assuming you should drain each cell to 0.8 v. measured with no load. With no load, you’re just measuring surface charge, not true charge state. So I think that the target discharge state must be measured with a light load, 50 ma. for a sub-C cell.

It’s a tiresome endeavor to try to externally discharge a tool battery pack (e.g. 12 v, with 10 NiCl cells in it) to the above recommended 0.8 v. per cell. After a period of use, cells seem to have very different charge capacities. Not knowing whether prolonged charge reversal would hurt the weaker cells, I’ve been reluctant to keep even a slow discharge (C/40, where C = charge capacity of cell) on a pack for the 30+ hours it might take to fully drain the stronger cells in the pack. Here’s my ‘current’ protocol for pack conditioning:

  • use up the pack’s charge with the tool or device, to the point it’s depleted.

  •  open pack so you can measure each cell’s remaining charge under light load (C/40 or less; for typical 1.2 v. sub-C cell this would be 50 ma., approx. 22 ohm load); some will be at 0, many will have >1.1 v.

  • for any that still give you >0.8 v., wire each cell to its own 22 ohm 1 w. resistor, keep load on until voltage is < 0.8 v. under this load.

  • do a test recharge on pack as usual; let sit a few days and test each cell again as above; those that are below 1.24 v. probably are self-discharging and should be replaced.

  • replacing individual cells in pack is tricky to do, but possible. I don’t have the spot welder you should have, but I’ve had luck using a 250 w. soldering gun & copper strips to attach new cells. Careful prep of surface, pre-tinning attachment spots, applying minimum necessary heat has worked so far. To keep all cells in a pack as age-matched as possible, I’ll try to combine the good cells from 2 old faulty packs to make one good one.

  • keep pack in discharged state until needed; don’t keep packs fully charged and unused for months at a time.

If there are errors here, I’m happy to have them corrected by someone with more knowledge.

On August 5, 2012 at 1:45am
Arek wrote:

Hello again.

I gave the current at which there is no polarity reversal for destroying cells that are in series.
Very supportive of Mr.. Isidor to do a deep discharge from the beginning of a new battery life is very, very prolonged his life.
Unfortunately, cells that have internal short circuit can not be saved, although their performance slightly increases, it will never get rid of no fault, and the battery will discharge itself.
My oldest AA Ni-cd are now 14 years old and about 540 mAh to 600 mAh her ​​when they were new. no longer have such a low internal resistance and faster to unload but still hold 50% charge after about 40 days.
Modern Ni-Cd cells are not as good and will not live as long as manufacturers design them specifically worse. But always appropriate treatment can be extended several times of their lives in good condition.
Of course, while charging the battery must be cool, if it heats up the charge current is too high.
Developed by the Soviet army for the cell current is 120mA SC for the maximum duration of life without regard to capacity as more capacious goals less accept over-charge.
For cell-C 160mA and 350mA-D cell. However, the current welfare and civilian customers forced to design a fast charger because posiadli money and charging time was the most important.
In 1970 one AA cell in the socialist countries cost about 1/10 the average salary. The recipients were only military users. Produced very little, the price was very high and therefore had to be a lifetime maximum.

On August 5, 2012 at 1:52am
Arek wrote:

posiadli - have.

For AA-cell 45-50mA, for F-cell 700 mA (military battery for radio).

On March 17, 2013 at 5:45pm
mike wrote:

“a battery analyzer featuring exercise and recondition costing US$2,500 would return the investment in less than one month on battery savings alone.”

I’m thinking that’s stretching things. How many cells (or packs - batteries) a day can this device recondition? The graph shows a 3 hour period. Unless it can handle multiple packs at a time, that’s 8 per day - 240 per month, way less than the 2600 batteries in the study.

On May 13, 2013 at 11:30am
Eric J wrote:

Mike, I bet it sure would pay off in a month for the U.S. Navy (that’s the statement they were making. Not for your average consumer of course). They probably have guys mistreating and tossing batteries left and right when they don’t hold a perfect charge anymore. Can’t really blame ‘em for tossing ‘em if it’s something that might save their lives.

On July 5, 2013 at 2:20pm

After spending about 2 months + non stop online learning about nicd and other battery types,and brutally learning the lesson of the battery voltage that refuses to die.ill give you this example of how i would discharge an 18v cordless tool battery pack.

i would charge the battery,use it in the tool till there is a noticeable drop in power output,take it out of the tool,connect a 1000 omh resistor and 6 leds at 3.6v each blue or white and let the battery run until it totally died,then unhook the leds and short the battery with the 1000 ohm resistor and put it in storage.

On July 6, 2013 at 7:18am
COburner wrote:

P.O. Titan: are you measuring discharged voltage under a small load (C/20-50)? No load voltage for most types of cells tells you almost nothing of the true state of charge.

As written above, you’re safe to discharge sub-C cell packs at 50 mA, which would be about 400 ohm load. I don’t see the point of leaving the 1000 ohm load on the fully discharged pack either.

I’m now trying out a smart charger that can put cells thru conditioning cycles, test capacity using charge/DC cycle, charge at various currents, and measure cell resistance. Generic Chinese maker and cheap, but I’m not going to recommend until I’ve tested further.

On July 8, 2013 at 8:05pm
PO TITAN wrote:

all i do all day is work on stuff like batteries.im going to tell you what i know and what i think.i know that when a nicd is fully discharged the voltage drops to 0 under load,any load pretty much,and if you short out the battery like nasa does when they store them the voltage is 0 and it stays that way.after you remove the short the voltage quickly climbs back to close to normal voltage 1.2+- even after days of being let shorted .according to everything iv seen the best plan is to drain the battery fast and hard then drain it as slow as possible then short it out-when the danger of over heating ect is no longer present.i believe from my research that a nicd is fundamentally unstable and that this is the reason for long life (electrode regeneration especially on the cadmium side) but that when the battery is simply left lying around discharged or charged fluctuations in the open circuit voltage lead to crystal growth/distortions.if im correct eventually all nicd will short out? it would naturally stabilize the environment inside the cell.

On August 16, 2013 at 2:40pm
PO TITAN wrote:

as a follow up to my previous post’s,i took a brand new 9.6v nicd battery pack to a cordless drill and hooked 3 leds to it.it took 9 hours to charge and with a 1000ohm resistor it literally was still discharging like 2+ weeks later.i stopped it around 7v and if you left the pack sitting the voltage would climb to only about 8v but after charging again the voltage climbed back up to 10v,the initial level of the brand new pack.iv recently read papers online that say that leaving a nicd to self discharge causes crystal growth,it also recommended not leaving the pack open circuit.My strategy now is to just put enough leds together to match the voltage of the pack and let it discharge,resistors aren’t really necessary because the voltage drop on the pack controls current flow.it may take multiple sets of leds to fully discharge the pack down to 0.Example 18v pack 6 leds voltage drops to 12,connect 4 leds ect.Im now considering high voltage pulse standby float charging.

On September 19, 2013 at 9:30am
martin borjas wrote:

I had a dead battery this a.m. and put my charger on. about 5 ninutes latter I unhookeed the negative and noticed the volts on the charger climb. what is up with this?

On September 21, 2013 at 8:43pm
po titan wrote:

it’s either something weird about your charger or it sounds like what i described above the voltage of a totally dead battery is like 1.12-1.16.

a good tip to add is that if you leave a battery shorted for along time it will leak,i had 2 AA nicds leak badly.I use a breadboard and i remove 6 5mm white leds from an 18v battery 1 at a time until it is down as low as possible.the voltage will stay low but once i charge again it goes back up to normal like 20v or so.job finished in my book.

On October 29, 2013 at 2:47am
Arek wrote:

Welcome COburner .

Surely 0.4 V is measured under load.
This is certainly a very small current .

Good exercise loading - unloading can take several weeks.
It is often not cost-effective , I performed only for research purposes .

If the cell is susceptible to repair, it ‘s been two cycles of very deep discharge will significantly improve its condition .
Unfortunately, the old cells , very worn out will not be a good fix .
The electrolyte is an old and often evaporate as a result of overloading .

Repair should link misused or old that have long lay unused .

Of course, even for cell 50mA high power SC will reverse polarity sensitive . But I will not damage the electrodes and the electrolyte.
Mass anti -pole assume no problem 50mA current and turns it into heat.

I have a Panasonic SC cell 1.9 Ah ( high power ) , they can take 150mA and no damage is , it can take up to several hours. Cells already have seven years and I do it once every two weeks.
This is a very good link. Currently have a 1700mAh at 0.2 C discharge.

Poor quality cells have no mass anti-pole, even 50mA can be reversed polarity and spoil the electrolyte and the electrode. Often, these cells swell with reversed polarity even a very small current.

A friend recently got a new cell weak brand. Cells without a name. Were sold in Poland for a professional company for emergency lighting.
The cells are 1.5 Ah high temperature
After 10 cycles to 1.1 Ah.
Load current of 0.5 A at - DV (- 1 mV).
Unloaded 0.5 A to 1V per cell.

Here, no battery memory effect only corrupts the very very poor quality.
It can not be repaired. I recently sailed electrolyte from the cells, leaving white coating of potassium hydroxide.

I recommend to use good cells because they have a real capacity and you can try to fix it when we use it properly.
Poor quality cells are highly perishable and are expensive to maintain because they still need to be replaced and monitored.

The biggest impact on life expectancy than - CD cells is the temperature , especially when loading . You have to use the DV systems responsive as possible .
The only draw back is that old or unused cell long may be too early detected as charged. After a few cycles of load cells normally.
Cells can not heat up above 30st.C during charging. If that is the charge current is too high or DV system is not sensitive .
Factory battery charger cordless tools are often very poorly loaded . very hot batteries for very low detection - DV .
When you load the correct charger can even 2-3 times to extend the life of the battery and its charging speed as it saves time, which previously served only to reload the cell and its heating .
The heated cell also loses some of the accumulated capacity and shorter working device powered by a battery .

Perfect charger detects (- DV) of ZERO.
Charging takes the shortest.
Loading cares very much about the life of the battery.
The battery is the most energy.

Even with 1C charge the battery remains cool.
High current also minimizes the formation of memory effect.
A lot of cycles can be performed. More than 0.1 C charge and no - DV (charger overnight).

This charger Zero DV very difficult to buy, I myself slowly so I make the ATmega8 (learn Bascom). My professional charger has a sensitivity of-3 mV. It’s a little too little for the best possible charge.

Ni-MH batteries, just not hot. Cycles are almost useless, a mere work them enough. Discharge cycle necessary when non-stop several dozen times discharge is only 30% and then charging. Very graceful batteries, just recharge the chilly temperature 30st.C max.
The ideal fast charging is 0.3 C and ZERO DV for high power cells.

On November 14, 2013 at 4:16am
Imre wrote:

Hi Arek,
I’m opening a battery recondition business in Ireland.I would like to contact you.my email is pathfinder0628@gmail.com
Regards Imre

On November 14, 2013 at 4:27am
Imre wrote:

Hi Arek.Im opening a battery reconditioning business in Ireland,would like to contact you.
Regards Imre

On March 22, 2014 at 9:40pm
jjgarett wrote:

Id like to add that the army pays 10 times the normal cost for items. The savings is easily seen. thanks

On July 9, 2014 at 6:27pm
Chuck wrote:

So from what I am reading a owner of nicad & nimh tools are set up to have battery failures if 1) they do not use their tools on a regular basis & 2) if you do not take the battery pack apart and check the cells individually and have slow deep drainage of cells at low currents. Is this true? I think my batteries do not last because of low usage and I charge them on a one hour charger only. Do these statements sound true and what can be done as a consumer to keep our batteries longer? Thanks

On November 8, 2014 at 6:37pm
Edward wrote:

the ni-cd battery are going to disappered…...............the ni-mh battery are replaced by lithium battery. what a pity, i have been working with ni battery for so many years

On March 3, 2015 at 8:59pm
Rick wrote:

On Nov. 8th, 2014 Edward wrote “the ni-cd battery are going to disappered…...............the ni-mh battery are replaced by lithium battery. what a pity, i have been working with ni battery for so many years”.  This is true, I’m sure but there are thousands of perfectly good Ni powered tools out there and replacement batteries, if priced right, will keep these tools in use for years to come.

On March 3, 2015 at 10:36pm
Edward wrote:

Hi Rick thank you for your encouragement,  please tell me the contact information if there are the NI battery need requirement zzrm316@163.com

On June 15, 2015 at 2:23pm
Larry Becque wrote:

There is a typo in this article:
why NiMH is less susceptible to memory than nickel-metal-hydride.

On September 24, 2015 at 7:07am
Alireza Ostad wrote:

please help me about Nickel-based Batteries:
Is there a way to Regeneration the nickel-cadmium batteries?

Thank you if you help me

On March 23, 2016 at 12:43pm
Jean-Paul Gignac wrote:

Hi everyone I’d like to share that i was successful at restoring an 18v battery pack (found in a battery recycling bin) to acceptable performance using this technique:
Charge the pack the best you can first then open it to reveal all the sub c cells.  LEAVE EVERYTHING INTACT. Short every cell to 0.7v using a diode and a resistor.  For my experiments i used the fattest diode i had in series with an 10ohm/10watt resistor.  Now i wouldn’t just stand there all night but i would solder maybe about 6 or 7 “shorts” careful not to overheat the cells by soldering the tabs instead and go back the next evening to do the next batch of cells.  I use my drill for odd jobs in the security industry and didn’t have to charge that battery for 2 weeks.  This technique is from trial and error.  Enjoy

On April 5, 2016 at 6:41am
Mike wrote:

I used the 15ma discharge rate instead of the 50ma discharge rate

on the first I was using a 150ohm resistor and the voltage dropped down to 3v on an 8 cell pack… I change that for a 500ohm resistor and the voltage is 7v and it’s actually getting hotter then the 150ohm resistor! I’m guessing that the charge in the pack seems to hit a wall because of reverse voltage… although I does stablize back upto 9.6v (1.2v/cell) once it’s an open circuit so all the cells must be around that voltage?

On April 7, 2016 at 5:05am
Mike wrote:

I discharged the pack to 4v (~0.5v/cell) using a 510ohm resistor and recharged it last night and it seems to have a much more gradual discharge curve and it lasted longer

thanks for the tips smile

On July 19, 2016 at 6:39pm
Wayne Robey wrote:

I have a very strange problem restoring old flooded pocket plate NiCd cells. The electrolyte becomes highly carbonated by exposure to air and some say oxidation of carbon in the plates. My thought was to react it with calcium hydroxide. This takes a long time due to the solubility of the Calcium hydroxide in electrolyte of about 200 ppm but it can be done. Recalling the warning to prevent trace contamination of the electrolyte with sulfate (to prevent corrosion of the pocket plates) I tried removing trace sulfate by reacting it with barium hydroxide (That should give a barium sulfate precipitate) till there is no precipitate formed with addition of barium hydroxide. .Then adding a bit of old electrolyte will precipitate excess barium and calcium. The problem is that when adding the barium hydroxide, a huge amount is required. Checking what was said to be calcium hydroxide by adding a bit of water saturated with barium hydroxide to a saturated solution prepared from the alleged calcium hydroxide, there is no precipitate, so no sulfate. So the puzzle is why do I get a huge amount of precipitate when adding barium hydroxide to the reprocessed electrolyte. New electrolyte should have specific gravity of 1.190 gr./ml and consist of KOH dissolved in H2O, and LiOH.  The lithium hydroxide should be approximately 12 gr./liter of electrolyte. Consulting solubility info for barium compounds shows very poor solubility for barium chromate (BaCrO4), barium carbonate, barium iodate, barium maginate (BaMnO4), barium pyro phosphate, and barium sulfate.

On October 4, 2016 at 9:36pm
Chris Caudill wrote:

Observing, understanding, learning, practicing, refining, and repeating…
It never ends, but it’s so valuable…. Its a behavior.

On October 24, 2016 at 10:51am
dobe wrote:

One of the best way to prevent NiCd cells damage in a pack during full discharge from voltage reversal is to apply a schottky diode to each cell reversely (anode to [-] and vice versa) inside the pack.
For AA batery pack a 3 to 5 amp.schottky will be sufficient to hold small current such C/40 within the voltage reversal drawn not more than [-]0.25v. The more diode capacity used, the more cell safety from reversal. SMD diodes can be applied to minimize needed space.

hope this will help

-from Indonesia-

On December 16, 2016 at 8:46pm
Michael Nixon wrote:

“One of the best way to prevent NiCd cells damage in a pack during full discharge from voltage reversal is to apply a schottky diode to each cell reversely (anode to [-] and vice versa) inside the pack.
For AA batery pack a 3 to 5 amp.schottky will be sufficient to hold small current such C/40 within the voltage reversal drawn not more than [-]0.25v. The more diode capacity used, the more cell safety from reversal. SMD diodes can be applied to minimize needed space.”

Thank you - that is very interesting. I might perform some experiments, since I am recently into designing UPS systems for single board computers (like the Raspberry Pi) and I am avoiding li-ion technology for this - sticking with good old NiMH. Initial designs use a dumb trickle charger (I built a standalone one I can hook up to packs to do C/10 or C/20, but the device has a built in C/40 permanent one).

Later I want to add the ability for the device to be able to change the charge rate to a maximum of C/10 if the cell was deeply discharged, and later switch to C/40 and then C/100 once finished. Once I have that working, I want to add a maintenance mode. The idea is the UPS will (on user command) deliberately disconnect the mains power, run from battery until it is as dry as possible, switch back to mains and then apply a small load to the battery to bring it as low as possible without cell reversal, before initiating a very slow C/20 charge. Your information is very helpful for this idea!

On January 8, 2017 at 7:44am
Milton Winslow wrote:

Have read the above information. Trying to determine the best way to condition and maintain 6 cell 1800 math NiCd stick pack. We are not allowed to open the pack up. The discussion above saids it’s best to open packs up. If rules will no allow that what do you do?

On February 23, 2017 at 2:10pm
ebod wrote:

“way to condition and maintain 6 cell 1800 math NiCd stick pack. We are not allowed to open the pack up”

Since the problem on nickel cells series in a pack is its reversal voltage under over discharged condition, setting a minimum voltage limit of a stick pack to certain point as described on this article is the first thing to be considered. Otherwise, either to buy a new one or to create a replica.

On February 25, 2017 at 12:45pm
Wayne Robey wrote:

Pulse chargeing is promoted at the start of this article but there is no information on how to do it. What pulse width, rep rate and peak current would be best?

On May 19, 2017 at 3:26pm
Michael R. Cole wrote:

According to the IEEE Orange Book, Recommended Practice for Emergency and Standby Power Systems, memory also occurs in ALL batteries if the charger does not charge up the battery enough. The real reason why NiCd batteries in the 1970s and early 1980s had memory was because the chargers were FLOAT chargers that only restored part of what you drain from a battery.

For instance, a float charger only restores 85% of what you draw from a lead acid battery. If lets say you have a 200 AmpereHour lead acid central battery emergency lighting system and you only have a float charger connected to it. If you discharge 100 AHr you will only get back 85 AHr. If you do that again and again you will soon have a dead or nearly dead battery. It takes about 14 to 16 volts to fully recharge a 12 volt lead acid battery, what is known as an equalizing charge which deliberate slow overcharging to bring all the cells up to the same level. Does use water. Sealed cells that have a catalyst for recombining hydrogen and oxygen can take a very SLOW overcharge but be careful. Most automotive electrical systems no longer do this to reduce water consumption by the battery. About once every 3 to 6 months you need to connect to your car a 6 amp charger that will deliver 1/4 amp at 16 volts. A few hours after that the battery should ( but may not be ) fully charged. Lead calcium low water consumption batteries can take up to a week to reach full charge because sticking in the last 25% of full charge is very difficult and slow. When fully charged

For a nickel iron battery it takes 17 to 18 volts to fully recharge a 12 volt battery. A float charger will only restore 65% of what is drained from a NiFe battery.

Regardless of battery type you need one of the following:

1. For lead acid and nickel cadmium, nickel metal hydride, and nickel iron tom which you can add water a float/equalize switch that you can use to deliberately overcharge and equalize the battery. For some stationary systems you might need a double throw switch to isolate the bank under an equalizing charge so as to avoid the overvoltage going into loads and overburdening the equalizing charger.

2. If a car will be parked for a long time a solar charger about 15 watts and an open circuit voltage of 18 to 20 volts will work just dandy. I did this when I was in a nursing home recovering from a broken left heel bone.

3. For NiCd and NiMH sealed cells a constant current charger that looks for a DECREASE ( negative delta V ) right before the battery reaches full charge. Tenergy’s chargers such as the model 01027 for 12 to 18 volt batteries up to 5.5 AHr will do this. After the 500 mA full rate charge it applies a 50 mA 30 volt equalizing charge for a few hours up to a total time of 15 hours.

I also have a Bachelor’s degree in Electrical Engineering/Physics

Michael R. Cole, Ohio elec. Contractor Lic. No. EL45,008

On July 17, 2017 at 1:05am
danielkr wrote:

This is for all the commentators before me:  Y’all have been an awesome read.  Thanks for keeping the comments on topic and sharing your wealth of experience and knowledge.  I have learned so much this evening.  Of course I have just spoiled its purity but I felt that the expression of appreciation could affect future commentating in a positive manner.  Sincerely, thank you all.

On August 3, 2017 at 1:12am
Dexterwise wrote:

This is the most interesting article I have ever read on batteries.

On August 3, 2017 at 1:52pm
Michael Cole wrote:

Charge - discharge tests that I have run on NEW nickel metal hydride batteries shows that you might need to do 3 or 4 full discharge recharge cycles to bring a new battery up to full capacity. Full discharge is to run it down to 1/3rd of rated voltage 0.4 volts per

Somewhere else somebody made the same comment that a new NiMH battery needs 3 or 4 full discharge recharge cycles to develop full capacity. My experiments very this.

In other words, they thrive on work. According to the Gulf Coast Batteries website about once every 2 months you need to fully discharge a NiMH battery.

What I use for discharge are series strings of 3156 or 3155 ( about 80% wattage of 3156 ) with 1 bulb for each 6 volts of battery so that the lamps operate at 50% voltage. Just make sure that you let the battery cool off before recharging.

The Gulf Coast Batteries battery internals ( guts ) kits for Black & Decker betteries using 3.8 AHr Tenergy NiMH cells have a 3rd prong for a thermistor ( temperature sensor that the B&D rapid chargers such as the BDCCN24 and the BDFC24 can sense so that they do not overheat the batteries. Most B&D slow chargers and the Tenergy 01027 do not have this capability. The Tenergy 01027 does have its own thermistor but putting it into contact with cells without unscrewing the lid is difficult. By the time you pop the lid that bettery has cooled down to some extent. Better of watching TV for half an hour.

On December 19, 2017 at 5:03pm
Frank Viola wrote:

I get a lot of “Donated” cordless Products when someone replaces them.  When recharging a pack, there are usually a few cells which remain at Zero Volts, no matter how long on charge.  I believe the Crystals have pierced the separator, and have created an internal Short.  I’ve had lots of success in “Reviving” these cells by “Zapping” them with a 7.2-18 Volt Nicad pack for a Half Second or so, which I assume Blows away the internal SHORT, and allows the batter to again accept a charge.  Has anyone ever tryed this before?

On December 21, 2017 at 12:21am
Wayne Robey wrote:

If you can get to the individual shorted cell, 2.5 volts is sufficient and I would current limit it through a resistor and monitor the voltage on the cell being treated. When the voltage exceeds 1.8 volts or stabilizes around 1.5 volts, I discontinue the charge and if the voltage does not fall below 1.2 volts, put it on standard charge. If no improvement is seen in 2 seconds, increasing the current may be good. The harder it is to revive, the higher the probability that the problem will soon recur.

On March 17, 2018 at 7:35am
Douglas D Goncz A.A.S. M.E.T. wrote:

I use exclusively separated cell rechargeable NiMH and NiCd battery pack and recondition with a smart charger that can fast charge a cell, dicharge and charge a cell, or cycle a cell repeatedly until capacity “levels off” to an unstated tolereance. I am very happy with my results and don’t mind paying the volume penalty. The weight penalty isn’t significant.

I use the Black and Deck 4AA alkaline screwdriver for example and on 4AA NiCd the perormance is not spectacular…but I never run out. On 4 NiMH the performance is fine.

I recommend the separated cell / smart charger / cell holder strategy.


On March 22, 2018 at 10:38am
Murray Hill wrote:

I have an E-Bike It cost me 700.00 $ a year .I would like a way to recondition all 7 batteries PLEASE !!!!!!!!!!  THANKS   Murray

On March 23, 2018 at 4:01am
Wayne Robey wrote:

Removing shorts (perhaps multiple times) while cycling them from full charge to discharged with individual cells held shorted for 24 hours (short the sell when the voltage falls below .3 volts) for at least 2 cycles is about the best that can be done. Sometimes the worst cells benefit from more cycles, sometimes they don’t. There was a article on this in Home Power several years ago.

On March 24, 2018 at 4:10am
Wayne Robey wrote:

I should have added that after the article in Home Power was published, further cycling of then poor cells produced improvement but I have had many that could not be improved at all. If you are not well equipt to do the charge/discharge cycles, you may consider one in a series of chargers/dischargers the most flexible of which is seen at https://hobbyking.com/en_us/0620-20a-300w-balance-charger-version-2.html
(I own one)

On March 26, 2018 at 10:39am
Douglas D Goncz A.A.S. M.E.T. wrote:

Here is the smart charger I use to keep my cell-based packs in prime condition:


I do *so* hate wasting a pack due to a cell drift.
Cell selection methods of pack reconditioning seem heroic compared to simply unloading all cells, selecting Refresh mode four at a time, and reloading all reconditioned cells.


On June 23, 2018 at 6:48pm
ken dias wrote:

My 18VDC battery pack cannot be opened as it is sealed. Hence many of the comments relating to separating the cells are not relevant. Us there any way to get my battery to work? Thanks

On September 15, 2018 at 3:58pm
fon parn wrote:

I discharge my ni-cd to 0v then give voltage backwards for 3 minutes with a 12v/10w light bulb in series, then let it cool down, then apply charging

On October 2, 2018 at 12:34am
Mahan wrote:

I have some saft ni-cd batteries. this batteries have worked for 25 years. now the capacity is lost. how can i revive them?

On November 16, 2018 at 12:33am
Fariz wrote:

I have few NiCd batteries that have been stored for a year without any maintenance. When I test the battery capacity for a few cycle, the capacity keep lower and lower. For example, the 1st capacity test (charge and discharge) I get 1888mAh capacity. The 2nd cycle, it down to 1780mAh, the 3rd cycle it down to 1750mAh and so on. Is it due the crystalline formation problem? Did I need to do the recondition in order to get back the actual capacity?

Thank you.


On November 18, 2018 at 1:52am
Wayne Robey wrote:

Capacity loss due to shallow cycling can be recovered by deep cycling but not much can be recovered if it is due to long term storage. I have seen this effect of capacity being highest on the first cycle of a battery left open circuit for a long time but also found it hard to get a consistent capacity measurement when experimenting with old cells. As one example, I had some vented NiCds removed from power backup service and allowed to stand about 25 years. I refilled them with new electrolyte, charged them at C/10 rate to 1.6C and checked capacity. Of the 14, 10 were at or above rated capacity, 1 was of no use, and the others slightly low. Cycling did them little good and repeating the capacity measurement on the 13 useful ones after a 1.6C charge gave lower capacity for the 10 best ones. I have no idea why.