# A Simple Step to Revive a Dead Ni-MH Battery

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Hello,

This is my first instructable. In this instructable i will show to all how to revive a dead battery( means the battery wont charge and will show 0V reading).

A few deays back i bought a pack of Ni-MH battery of 2400mAh. But some in them was not charging. So i had to search a lot to find a proper solution to revive the battery. So let me tell you the steps through which i got them working again.

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## Step 1: Cheking the Battery

First let us check weather the battery has any juice left in them after charging them for a while so that we can confirm that the battery is dead.

Here in the image you can see a dead Ni-MH battery.

## Step 2: Reviving the Battery

Next we must take a similar battery of the same mAh which is fully charged.Then we have to connect the positive terminal of the fully charged battery to the positive of the dead battery and similarly connect the negative terminals.

Let the batteries be connected for a few seconds almost 20-30 sec. Then immediately check the battery voltage of the dead battery, if u see a reading above the 0 value then you can be sure that the battery is revived.

If the battery is still dead try the step again, i had a problem with 1 battery which did not work for this step the first time, later after some 3 tries it worked and is good as new. If you are still having problem check weather you are using a full charge battery for reviving the dead one.

Ones the battery is revived charge it until it is full.

That's all for this instructable.

## Step 3: Explanation

"Some batteries die when a short developes between the positive and negative terminals of the battery This happens a lot with NiCd batteries and can happen with other chemistries. The short is caused by a metalic dendrite crystal. The electric charge between the two terminals of the battery encurages dendrite formation.

by connecting a fully charged battery to the dead shorted battery you willl get very high current flow through the dendrite. That will casue it to get hot and melt. Hopfully that breaks the short. Modern lithium ion batteries rarely short out in this way. Also lithium ion batteries are very sensitive to overcharging. If they overcharge they can catch fire . So I would not recommend this with lithium ion batteies." Thank you steven4872 for the explanation.

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## 31 Discussions

My battery was showing 1.2V, but my charger considered it bad. I charged it per your instructions, and the voltage ended up at 1.33V, and then my charger considered it still good. Thanks!

Many Thanks:

I received a \$50 "eBay Parts Only" iRobot Roomba 650 vacuum cleaner yesterday.
The iRobot OEM nicad battery was completely dead and measured 0 volts.

I connected
the positive to positive, negative to negative terminals from the 0
volt battery to a spare battery for 20 seconds resulting in the 0
voltage gaining a fractional value, just enough to activate the charger.
I put it in the Roomba and charged overnight.
Ran it until exhausted today for an hour and 53 minutes.
It is now charging normally on dock.

Nice one thanks bro worked great on one of my rc car batteries thanks again

Thanks for this insight. I had two AA Nimh in my Wii Remote, one had a NEGATIVE charge of -.71 volts. I thought I'd have to throw out the battery because my charger wouldn't charge it. I connected it like you said and left on for about 20 seconds. It was still negative, I did it again for another 30 seconds and voila! It was at .72 v positive. Then the charger would take over. Weird, but it worked - thanks again.

It worked for a dead 5000mAh pack - I revived it with a 2200mAh fully charged one. It took a mere 20 seconds. Thanks a lot!

This worked with Midland BATT5R .. A battery pack with 3 unknown Ni-MH inside !

I simply connected the output terminals to a similar 6V source and then the pack would recharge - Interesting - there are 2 sets of pickups / contact on the pack - 2 are used for charging within the radio and 2 are used for output - Checking with a volt meter I was getting a reading from the output terminals 6.3 Volts BUT there was no reading across the charging terminals 0.0 V !! .
I thinks Stephen4872 explanation about metalic dendrite crystal might explain a lott- I thought these batteries were complete gone ! -and was actually look on Ebay & Amazon for replacements when I happened across this site -

Thank you Paul1212 - you saved the day ..

Thank you so much for this Instructable! I easily revived 3 dead AA Ni-MH batteries. 2 worked after one 25-second cycle and 1 took two 25-second cycles. This is great considering I have a "green thumb" and didn't want to throw these away!

Is this really possible? If yes then only with ni-mh? I think you should post a video to clearly show that.

2 replies

I just fixed my 18V NiCad lawn trimmer battery using Paul's method. Easy way to think of this is that there is a fine wire jumper connected across the positive and negative terminals of your bad battery. The charger current tries to push electrons onto the negative terminal of your battery to charge it but the electrons just take the easiest path through the jumper and nothing takes place in the battery. When you "boost" the shorted battery (exactly as you boost a dead car battery) you cause lots of current to travel through the little jumper and it heats up and melts. Now when you hook up the charger the electrons have to enter the battery and cause the chemical reaction that stores them there.

I dont know about other batteries.. But Ni-Mh can be easily revived this. Sorry i dont have a video of it.. All my batteries got revived and is being used in my robot. So i dont have a dead battery to take a video..
The photo shows a dead battery being revived and we get an almost .8V output.

Hi, I bought a charger plus 4 rechargeable NI-MH Philips 2450 mAh seal, I had bad luck that one is defective, the value was 0 when I measured, I tried version of this article and it worked! Thanks for the nice tutorial, I saved the battery;)

This worked great for me with 2 cordless phone batteries and a couple of jumper wires. I had to fast-charge the bad one several times to get it up to a voltage where the regular charger would take over, but now it works fine. Thanks!

Whats the logic behind this? It makes no sense to me. You connected two batteries in parallel....to nothing. What am I missing here?

7 replies

Yes. This really works..
I have tried it myself.. I tought the photos proved am right..

Some batteries die when a short developes between the positive and negative terminals of the battery This happens a lot with NiCd batteries and can happen with other chemistries. The short is caused by a metalic dendrite crystal. The electric charge between the two terminals of the battery encurages dendrite formation.

by connecting a fully charged battery to the dead shorted battery you willl get very high current flow through the dendrite. That will casue it to get hot and melt. Hopfully that breaks the short.

Modern lithium ion batteries rarely short out in this way. Also lithium ion batteries are very sensitive to overcharging. If they overcharge they can catch fire . So I would not recommend this with lithium ion batteies.

Thank you for explaining it (I didn't how this was supposed to work), I think this should be mentioned in the instructable

I understand now, thanks to some of the other comments. This technique will only save batteries that have discharged from sitting due to being in the store for a long time.

The charger won't sense the cell if it has zero charge. When you connect the full cell to the empty one the full cell charges the empty one (a bit, enough).

Once it's partially charged the charger can charge it back up fully. It will work provided the 0v cell isn't damaged, provided it only self discharged because it's been standing on the shelf too long.

Alright, that makes a bit more sense. The part about the charger not recognizing it is pretty important. You are manually charging the battery using another battery to allow the charger to sense it. This method is not going to save a battery that has been through too many charge/disharge cycles.