BU-807: How to Restore Nickel-based Batteries

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?

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

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

Welcome.

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.
Regards
Arek.

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.

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.

posiadli - have.

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

“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.

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.

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.

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.

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.

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.

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?

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.

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.

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

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

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

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

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 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.

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

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

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

Thank you if you help me

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

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?

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

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.

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

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-

“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!

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?

“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.

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?

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