Possible to revive 1.2V Ni-MH battery?

[sofakng]

I've just purchased an R/C car for my son and it includes a very tiny 1.2V 80mAh Ni-MH battery that is reading 0.11v and won't charge using the included charger.

I'm going to try to get a replacement, but is it possible to try and revive this battery or charge it manually using a bench power supply?

[tunk]

You could try to use e.g. an 1k resistor in series with the cell, and set the PSU to 1.5V.

[wraper]

Charge it a little bit until voltage rises to 0.8-1V by small current from a current limited source. Like lab PSU or any PSU + current limiting resistor in series.

[sofakng]

You could try to use e.g. an 1k resistor in series with the cell, and set the PSU to 1.5V.

Trying it now.  Thanks!

[sofakng]

Charge it a little bit until voltage rises to 0.8-1V by small current from a current limited source. Like lab PSU or any PSU + current limiting resistor in series.

Thanks!  I'm trying tunk's suggestion of 1.5V with 1K resistor.  It sounds like you are suggesting the same?

[wraper]

Charge it a little bit until voltage rises to 0.8-1V by small current from a current limited source. Like lab PSU or any PSU + current limiting resistor in series.

Thanks!  I'm trying tunk's suggestion of 1.5V with 1K resistor.  It sounds like you are suggesting the same?

I suggest charging it a little bit until it can be charged the normal way.

[sofakng]

Sorry, but what do you mean by charging it?

I'm using my bench psu (1.5V w/1K resistor) to attempt to charge it (until 0.8V or similar as you mentioned) and then I'll try to use the built-in charger it came with.

I did attempt to charge it using the built-in charger for about 6 hours with no luck.

[wraper]

I mean charge it for a few minutes until voltage rises and then charge it by a normal charger. Many chargers will not charge batteries which are totally flat.

[BillyO]

None of the suggestions given so far are really effective.  Look up "reflex charging" or "burp charging" for Ni-MH batteries.

[AndyBeez]

Yes, it is possible to revive a depleted NiMH battery, by charging and discharging, but there is a big but. NiMH cells have a limited 'practical' shelf life of around 5 to 7 years. If this battery was left uncharged for a few year's, it may be worthwhile replacing it. It was possibly not the best quality part to start with. Sounds like the kind of battery found in dollar store solar lights. Any idea how old the toy is? A chip date code should tell you within the year when the toy left the factory.

[sofakng]

It appears to be fixed!

I followed tunk's idea and after a few minutes it measured 1.1V and then the included charger detected it and finished it.  I'm not sure if the battery will keep a charge, but regardless my son is incredibly happy. 

Thanks everybody!

[sofakng]

Yes, it is possible to revive a depleted NiMH battery, by charging and discharging, but there is a big but. NiMH cells have a limited 'practical' shelf life of around 5 to 7 years. If this battery was left uncharged for a few year's, it may be worthwhile replacing it. It was possibly not the best quality part to start with. Sounds like the kind of battery found in dollar store solar lights. Any idea how old the toy is? A chip date code should tell you within the year when the toy left the factory.

Yeah, it's probably been sitting on the shelf.  I can't find a date on the battery but I see a few replacements online which I think might fit if needed.

[wraper]

None of the suggestions given so far are really effective.  Look up "reflex charging" or "burp charging" for Ni-MH batteries.

Really? What you are suggesting is not even applicable to charging a battery which was discharged totally flat. Not to say the whole reflex charging thing is not proved to work even for its intended use.

[kripton2035]

I have an ELV branded "ALC8500" battery charger. it has a "revive" option for nimh batteries that is quite effective
when the voltage os too low on these cells, I use it and it almost always revives it.
it seems they apply some high voltage (around 60-80v) short pulses to do this.

[IanB]

If you have a very low voltage NiMH or NiCd cell, then trickle charging it with 1 to 5 mA or so to bring the voltage up is a standard technique to revive it.

I used this technique when I had an unchargeable Ryobi NiCd battery pack that had been sitting on the shelf for too long. It's not the most useful battery, but at least it works now.

[wraper]

I have an ELV branded "ALC8500" battery charger. it has a "revive" option for nimh batteries that is quite effective
when the voltage os too low on these cells, I use it and it almost always revives it.
it seems they apply some high voltage (around 60-80v) short pulses to do this.

I don't know particular charger but most likely the only thing it does is bypassing normal mode which cannot detect flat batteries without applying some voltage to the terminals first. Maybe uses different charging current than normally. 60-80V is not possible. First of all it would make such charger unsafe. Secondly you simply cannot rise voltage to such level with a battery connected unless it's so dead that has so high ESR its basically open circuit.

[BillyO]

None of the suggestions given so far are really effective.  Look up "reflex charging" or "burp charging" for Ni-MH batteries.

Really?

Yes really.  The process helps clear crystals that form in the electrolyte.  The reason it is likely totally flat is due to the very high self discharge caused by the crystal growth.  You can still charge the cell, but it will quickly go flat again.

But I wish you had not told me it didn't work as it's been working fine for the last 35 years.  Now it will probably not work anymore!  Darn!!!


The below also applies to Ni-MH.  To a lesser degree than NiCd, but applies all the same.  There are other references.  Go look for them.
https://batteryuniversity.com/article/bu-807-how-to-restore-nickel-based-batteries

[wraper]

None of the suggestions given so far are really effective.  Look up "reflex charging" or "burp charging" for Ni-MH batteries.

Really?

Yes really.  The process help clear crystals that form in the electrolyte.

I wish you had not told me it didn't work as it's been working fine for the last 35 years.  Now it will probably not work anymore!  Darn!!!

https://batteryuniversity.com/article/bu-807-how-to-restore-nickel-based-batteries

1. Battery univercity is garbage source of information which is filled with a lot of dubious and incorrect information. I would not trust anything written there without verifying with another source. 2. This topic is about original charger not charging a battery which was drained totally flat, not restoring a badly performing battery. 3. The article over the link you gave does not even mention restoring batteries which were drained flat. 4. That article is not even about anything remotely resembling "reflex charging" or "burp charging".

[magic]

The idea is to apply short pulses of high current to clear internal shorts due to growth of metal dendrites in reverse-charged cells of overdischarged multi-cell packs. I seem to recall that it was a legitimate problem in NiCd, not sure if in NiMH, but I don't recall finding any legitimate source confirming that the method really works.

Somewhere I have a box of NiCd cells pulled from an abused pack (my father's cordless drill ) which I intended to experiment with, but never got to actually doing it.


None of it has anything to do with a battery which self-discharged to zero by sitting on the shelf.
Unless there are some other failure mechanisms I don't know about.

[james_s]

There is no indication at this point that there are any shorts or defects, it may just be an older technology NiMH battery that is not low-self-discharge, or it may have been left plugged into the toy and gradually drained completely flat. In this case there is nothing wrong with the battery, it just needs to be charged up enough for the charger to see it.

[BillyO]

1. Battery univercity is garbage source of information which is filled with a lot of dubious and incorrect information. I would not trust anything written there without verifying with another source. 2. This topic is about original charger not charging a battery which was drained totally flat, not restoring a badly performing battery. 3. The article over the link you gave does not even mention restoring batteries which were drained flat. 4. That article is not even about anything remotely resembling "reflex charging" or "burp charging".

That article does explain, you don't understand.

Besides, I'm not here to educate you.  You can do that yourself and as I said there are many other references.

At this point I'll give you the last word.  Have a nice day.

I changed my mind .. I get tired of people on the internet expounding from a position of deep ignorance.

1)  The battery in question was at 0.11V.  The only way it could get that low was through self-discharge.  It would have stopped powering the car LONG before reaching 0.11.

2) Ni based batteries, if left at such a low state of charge for any length of time (just a few days is enough) only get worse.  Their capacity drops precipitously as their electrolyte forms large crystals, and because their capacity is so diminished they will appear to charge quickly (as is the case here) but will not hold the charge.

3) This problem can be fixed to some extent by using reflex charging.  It will help remove some of the crystal build-up (but not all) and allow the battery to re-gain some capacity.  Putting a high value resistor on it for a while until it can trigger the original charger will NOT fix it.  If it only has 5% capacity before your "process" it will still only have 5% capacity after it.  In fact, it can make things worse.

4) That article explains what happens to Ni chemistry batteries.  You were supposed to put 1 and 1 together and get two.  You didn't.

5) I already mentioned reflex/burp charging.  It's up to YOU to read about it and understand what it does.  It's not up to me to go into such details on a forum for your benefit.

6) I honestly don't care about the original charger.  It's not going to help.  I told the OP what he needs to do.

7) Dunning and Kruger are looking for subjects.  Give them a call.

Now I'm done.

[wraper]

That article does explain, you don't understand.

Besides, I'm not here to educate you.  You can do that yourself and as I said there are many other references.

At this point I'll give you the last word.  Have a nice day.

You barged in and said what we suggested is of no use (it did actually work). Article you linked explains something entirely different, not related to reflex charging at all. It's about how to restore NiCd cells affected by a memory effect by discharging at a small current down to a lower than normal voltage. Did you even read it yourself? Reflex charging is supposed to allow high charge rate by applying very short high current discharge pulses during charging.

[BillyO]

You barged in and said what we suggested is of no use (it did actually work).

It wasn't and no, it really didn't.  See my update above  Time will tell.

[IanB]

1)  The battery in question was at 0.11V.  The only way it could get that low was through self-discharge.  It would have stopped powering the car LONG before reaching 0.11.

2) Ni based batteries, if left at such a low state of charge for any length of time (just a few days is enough) only get worse.  Their capacity drops precipitously as their electrolyte forms large crystals, and because their capacity is so diminished they will appear to charge quickly (as is the case here) but will not hold the charge.

I really do not believe this. There is a technical paper by NASA concerning the long term storage and stability of NiCd batteries intended for space usage.

Their recommendation is to discharge NiCd cells down to zero volts, to short the + and - terminals together, and then to store them this way until needed. It seems they can be stored for years without degradation using this technique.

This may not be true for NiMH cells and so it is not certain the same will apply.

However, crystal growth requires electrical current to deposit ions on the crystal lattice, and electrical current requires voltage and energy to drive it. If a cell is in the lowest possible energy state when discharged to zero volts, there is very little energy available to drive harmful processes inside the cell.

[kripton2035]

I have an ELV branded "ALC8500" battery charger. it has a "revive" option for nimh batteries that is quite effective
when the voltage os too low on these cells, I use it and it almost always revives it.
it seems they apply some high voltage (around 60-80v) short pulses to do this.

I don't know particular charger but most likely the only thing it does is bypassing normal mode which cannot detect flat batteries without applying some voltage to the terminals first. Maybe uses different charging current than normally. 60-80V is not possible. First of all it would make such charger unsafe. Secondly you simply cannot rise voltage to such level with a battery connected unless it's so dead that has so high ESR its basically open circuit.

when the revive process is happening, you can actually hear and see sparks on the battery terminals...
next time I have a battery candidate, I will try to record the voltages on the battery during the process.