Ni-MH batteries no longer charging

[Wozzaaah]

I've got loads of AA Ni-MH batteries that refuse to charge in my usual charger that obviously performs some sort of check before attempting to charge them though they'll charge fine (and seem to hold a charge) if I leave them in my pound shop USB charger.
It's probably my fault for not using them properly, i.e not using them in any particular order so some have stayed flat for a long time.

What is it that tells the charger not to charge them when they seem perfectly ok and other than doing something daft like putting a higher voltage through them to 'shock' them back to life is there any way of getting them to charge normally again?

 

[harvey639]

I have seem people zap them with 80 amps using a stick welder

 

[Wozzaaah]

Did you see them again though?
I have heard about zapping them but I'm not sure tbh, I may try it on one and see what happens.

 

[brightspark]

just give them a quick touch with a car battery cross polarity and charge them up it works on most battries nowt to loose

 

[armalites]

Thee are loads of people on ebay who list power tool battery repair.

On power tool batteries Ni-Cd and what you need to do is set up a rig that has higher voltage.

For 18v batteries I use 2 car batteries in series so 24v

Put a meter on the battery first and check the +ve -ve and the voltage.

Connect the -ve to the -ve on the car batteries then connect the +ve to one and then tap the connection on the other +ve a few times. It will arc but it will it will normally revive the battery.

Check the voltage repeat if needed then put on charge.

Early power tool batteries are only standard indutrial cells in a package so this process should work on single batteries too.

I have taken to buying hybrid batteries that hold their charge and bought a Ansman charger where each slot is individually controlled.

The batteries charge better and last longer than on a timed charge

 

[Marc.]

I read about the 'zapping' thing a while ago when my battery for my 24v bosch cordless dril wasnt holding a charge. It wouldnt hold a charge and the damn thing would not charge after that either! There are youtube vids etc on how to zap the batteries, but to be honest, theyre half dead by then anyhow and even if they do 'recover' the battery for a while, it wouldnt be long before they started to play up again.

 

[Welderpaul]

Are we not talking about AA batteries rather than power tool batteries?

 

[hotrodder]

The 'zapping' thing is for NiCds, downright dangerous with Li-ion dunno where NiMh fall between them... not as fussy as Li-ion regarding charging but they don't fail in the same way as NiCds so there's no dendrites/'memory effect' or whatever it is that zapping 'repairs'

Powertool battery packs are still composed of a bunch of individual cells connected up in much the same way as AA batteries. There's just more of them to bump the voltage up and they're a different size

 

[Wozzaaah]

Yes, I'm talking AA, not power tool batteries.
I'm just curious as to why the charger refuses to charge them though if I trickle charge them in that USB charger they seem fine.
Admittedly, I've not tested them extensively, I just put them in whatever needs them until they're exhausted again so though they charge they may not be holding a full charge.

 

[hotrodder]

Charging NiCds versus NiMh... http://www.greenbatteries.com/bachfa.html#NiCD%20charger%20for%20NiMH%20batteries

 

[Marc.]

My apologies, its the drink early on in the evening! I'll get me coat.....

 

[pidgeon chit welder]

Wozzah , nicads of all descriptions build up a resistance to charging over their average life of around 1,000 charges .
The higher DC voltage kick start mentioned CAN break the resistance down and allow a few more charges but it does not last for long .

Years ago during my electronics training era I was advised to always fully discharge the batteries before attempting recharge by using an appropiate light bulb so that the battery voltage was down to less than half the nominal voltage then recharge to get maximum long life out of them .

If you keep trying to or recharging a partialy discharged Nicad it will develop the resistance stage much earlier in it's life .. a bit like having a set of stairs adding an extra step level of resistance to overcome each time you connect it up for charging

 

[pedrobedro]

I tried zapping the 12v nicad battery in my old firestorm drill and it revived it for a couple of weeks then it went back to dying within the hour.We have some AA nicad batteries for a camera which have lasted years, they are charged up when they need it and used till they are flat again and it seems to do them no harm.

 

[Sean]

back to OP. Think "pound shop charger" may have something to do with it get a smart charger I use a "Tronic" one which runs off the van 12v as well as mains

 

[voipio]

NiMH cells have a habit of developing a relatively high internal resistance after a few dozen charge cycles and the smart charger detects this as a faulty cell. The PoundShop charger probably doesn't perform any checks. When NiMH cells begin to behave this way, although they will take charge, their performance will be below par in high current applications and their useful days are numbered.

 

[Wozzaaah]

back to OP. Think "pound shop charger" may have something to do with it get a smart charger I use a "Tronic" one which runs off the van 12v as well as mains

You seem to have missed the bit in my first post where i said I have a smart charger.
They were dud long before I bought the pound shop charger.
I bought the charger knowing it would charge without performing any sort of health check.

 

[shenion]

The smart charger may test the batts. If it sees the NiMh batts having a higher than normal resistance, then it may see them as dry cells and not charge them.

As NiMh batts get old, they develop more resistance.

The zap fix may help a bit, but is usually for fixing shorted cells. I used to use a large capacitor charged from a DC power supply.

 

[Sean]

You seem to have missed the bit in my first post where i said I have a smart charger.
They were dud long before I bought the pound shop charger.
I bought the charger knowing it would charge without performing any sort of health check.

Ah

 

[500e]

http://www.ka7oei.com/nicds.html
The other thing to remember there are good cells & c**p ones cheap rechargeable are usually not the best cell poor time in service & short life overall.
We use hundreds of cell packs in our radios & it is surprising on our charging system how many are not the capacity suggested when new.

http://www.cadex.com/prod_analyzers/

All you want to know about rechargeable's in depth

http://www.buchmann.ca/

 

[Wozzaaah]

Thanks all, some good info there.
I've just used an old ATX power supply to briefly put 12V through a couple to see if shocking them worked but it didn't.
They got very warm but as soon as I put them into the smart charger it says no go.
Having said that, 3x 5 second zaps each and they're now in my mouse and are working fine.
I probably have far too many anyway, I am sat here now looking at over 25 that aren't currently being used!