New NiMH Cells Run FLAT - Not Charging Anymore (only used twice)

[Gazoola]

Hi
My kids ran a toy dead flat. I think it was left on for days, with some fairly new 2500mAh Varta batteries in it.
I put them in my battery charger and it signalled that 3 of the 4 were faulty and failed to charge them. I have read that you shouldn't fully discharge batteries and my multimeter showed the voltages in these at about 30 mili volts!!

These batteries cost me about $20 for 4, so I want to find out a way to jump start them again, to put enough residual voltage in to let the smart charger continue.

OPTIONS:
Fix 1: Connect a 'failed' and a good battery in parallel, to put in the charger slot. Would effectively have a 1.2v 5000 mAH AA cell??

Fix 2: Buy a cheap dumb time based charger, and give the batteries an initial charge with that, then back in the smart charger.

Fix 3 : Use an old 3.4 v 500mA DC adapter to give the battery a 'jumpstart'. I found a mention of this on Google. Has anyone done this? Would the 3.4 volts be a problem for a 1.2v cell?

Fix 4: Running the batteries that flat (30mV) has rendered them FUBAR and no tricks or charger will help ???

All insight much appreciated!
Cheers
Gaz

 

[Mr Happy]

Re: New NiMH batteries (twice used) not charging anymore.

Hi,

:welcome:

Unfortunately your batteries may be damaged a little, but they do have some chance of recovery. You can try raising the voltage a little as you suggest and then the charger may accept them. Connecting one of the discharged batteries in parallel with a partly charged battery for a short time should do the trick. Try initially for a few seconds, then a few more seconds, then a minute or two. When the multimeter shows a voltage close to 1 V on the empty cells, try charging them again.

 

[TakeTheActive]

Re: New NiMH Cells Run FLAT - Not Charging Anymore (only used twice)

Hi...

:welcome: That's a pretty good / well-composed post for a Newbie! :goodjob:

How did you find CPF?

...My kids ran a toy dead flat. I think it was left on for days, with some fairly new 2500mAh Varta batteries in it...

Don't worry about it too much. One of CPF's Gurus did exactly that ON PURPOSE!

Interesting... but not recommended...​

...I put them in my battery charger and it signalled that 3 of the 4 were faulty and failed to charge them...

What's the manufacturer and model of your charger? (La Crosse, and its clones, are noted for rejecting cells under ~0.5VDC 'Open Circuit'.)

...OPTIONS:
Fix 1: Connect a 'failed' and a good battery in parallel, to put in the charger slot. Would effectively have a 1.2v 5000 mAH AA cell??

Fix 2: Buy a cheap dumb time based charger, and give the batteries an initial charge with that, then back in the smart charger.

Fix 3 : Use an old 3.4 v 500mA DC adapter to give the battery a 'jumpstart'. I found a mention of this on Google. Has anyone done this? Would the 3.4 volts be a problem for a 1.2v cell?

Fix 4: Running the batteries that flat (30mV) has rendered them FUBAR and no tricks or charger will help ???

COMMENTS:

1. Close. Connect them in parallel and let the GOOD cell charge up the BAD a little. DO NOT put both together into a charger!
   .
2. Good. It never hurts to have an 'Old-n-Slow' DUMB charger around. You can use it for 'Jump Starts' and also for ~0.1C / 16 Hour 'Forming Charges'.
   .
3. Also good. The goal is to get the BAD cell over ~0.5VDC O.C. - a few seconds on a DC train transformer also works.
   .
4. Nah! Read the first LINK above and report your progress.

BTW, I suggest that you EDIT your title to include more information for others to find when SEARCHing:

New NiMH Cells Run FLAT - Not Charging Anymore (only used twice)​

I'm going to suggest the same to SilverFox. :thinking:


Good Luck! :wave:

 

[Gazoola]

Re: New NiMH batteries (twice used) not charging anymore.

All fixed!

Thanks for the advice...

I ended up using the AC/DC adapter with an alligator clip and a couple of wires to give the 'faulty' batteries a jump start, for a second or so only and they now charge in my Rezap RBC883 http://www.rezap.com.au/

This charger which can refresh/charge alkalines has a lot of built in protection logic and I think rejecting fully drained cells may be part of this. Anyway at least the AC/DC adapter is an easy fix. I am heartened by the thread mentioned where the Eneloops were drained to last century, so hopefully mine are still fine.

BTW - I know little about electronics, so can anyone comment clearly on this...
Only when necessary, is is OK to use this Nokia AC/DC adapter to momentarily jump start my AA cell ?? - the specs of it are Output: 3.7v / 355mA / 1.3VA.
The current looks OK, but what about the volts?
If not I suppose I should use the good and bad battery in parallel trick right?
The reason I ask is that when charging, my Rezap RBC883 puts out only 1.4v at 250mA.

 

[Gazoola]

Re: New NiMH batteries (twice used) not charging anymore.

Hi,

:welcome:

Unfortunately your batteries may be damaged a little, but they do have some chance of recovery. You can try raising the voltage a little as you suggest and then the charger may accept them. Connecting one of the discharged batteries in parallel with a partly charged battery for a short time should do the trick. Try initially for a few seconds, then a few more seconds, then a minute or two. When the multimeter shows a voltage close to 1 V on the empty cells, try charging them again.

I like this gentle and gradual approach, probably safer and better for the cell if I wasn't so hasty with the DC adapter.

:welcome: That's a pretty good / well-composed post for a Newbie! :goodjob:

How did you find CPF?

Good old Google. I had been lurking for a bit and found there were some real cluey people here.

BTW, I suggest that you EDIT your title to include more information for others to find when SEARCHing:

New NiMH Cells Run FLAT - Not Charging Anymore (only used twice)​

I tried to modify the title with edit but it only allowed me to edit my post body not the title. It coud be due to the fact that I am new on the forum and I need to make 2 post before modifying such things - will try again soon.

 

[Mr Happy]

Re: New NiMH batteries (twice used) not charging anymore.

To edit the title I think you need to click the Go Advanced button after you enter the edit screen.

 

[shadowjk]

Re: New NiMH Cells Run FLAT - Not Charging Anymore (only used twice)

Don't worry about it too much. One of CPF's Gurus did exactly that ON PURPOSE!

Interesting... but not recommended...​

Though he only did that with a single-cell. In multi-cell applications you'll have polarity reversal on the weakest cells, which is most certainly hell of a lot harsher than depleting a single cell to 0.

 

[TakeTheActive]

Re: New NiMH batteries (twice used) not charging anymore.

...I ended up using the AC/DC adapter with an alligator clip and a couple of wires to give the 'faulty' batteries a jump start, for a second or so only and they now charge in my Rezap RBC883 http://www.rezap.com.au/...

:wow: That's one heck of a charger you got yourself there. If I still have the energy left, I want to check the Australian-to-US Exchange Rate later on - $118AU!!! I just read at least half of the online documentation and skimmed the rest and NOWHERE could I find the Charge Rates for the 4 channels listed. (Found 300mA for the USB and DC OUT ports)

• ...BTW - I know little about electronics, so can anyone comment clearly on this...
  Only when necessary, is is OK to use this Nokia AC/DC adapter to momentarily jump start my AA cell ?? - the specs of it are Output: 3.7v / 355mA / 1.3VA.
  The current looks OK, but what about the the volts?
  If not I suppose I should use the good and bad battery in parallel trick right?
  The reason I ask is that when charging, my Rezap RBC883 puts out only 1.4v at 250mA.

• I like this gentle and gradual approach, probably safer and better for the cell if I wasn't so hasty with the DC adapter...

A few seconds at OVER ~1.5-2.0VDC isn't going to matter a bit. If you CLICK on my Sig Line LINK and read through the CPF Archives, you'll find a GREAT post by jtr1962 where he discuses Charge Rates. You can safely charge an empty cell @ 4.0C (15-Minute Chargers) *UNTIL* heat begins to build (~70% SOC). A few seconds @ 3.7VDC is nothing. Plus, since the current available is so low (355mA), the output voltage of that adapter probably dropped anyway. One of the local Math Whiz / Engineering Types can explain it better but, bottom-line, don't worry.

Getting back to your Rezap RBC883 Charger, where did you find the "1.4v at 250mA"? I found:

Input Voltages: DC 12V, 2A Switching Power Adaptor (AC 100 - 240V 50/60Hz, 0.8A Max)​

which matches the Maha MH-C9000, so I would expect the Charge Rate of the individual channels to be similar, especially for charging C and D cells.

...I tried to modify the title with edit but it only allowed me to edit my post body not the title... - will try again
soon.

:thumbsup:

__________________________________________________​

My wife is constantly amazed at how much time-per-day I spend reading and answering questions on forums. When I mentioned I was "talking" to a fellow is Australia, she came up with a slew of questions:

1. How hot is it there today?
   .
2. How far are you from Steve Irwin's zoo?
   (i.e. where are you? IIRC, isn't the zoo in Queensland?)
   .
3. Is the zoo still open?

Thanks!

 

[TakeTheActive]

Re: New NiMH Cells Run FLAT - Not Charging Anymore (only used twice)

Though he only did that with a single-cell. In multi-cell applications you'll have polarity reversal on the weakest cells, which is most certainly hell of a lot harsher than depleting a single cell to 0.

Though, since his cells are new, perhaps they are very close in capacity so...

...As soon as I can convince my grandson that he needs to loan me one of his toys for some testing I will try some actual testing with a multi cell toy.

My thought is that the Eneloop cells are very close in capacity, so if they are charged in an independent channel charger, there should be little chance of reverse charging...

 

[Mr Happy]

Re: New NiMH batteries (twice used) not charging anymore.

That's one heck of a charger you got yourself there. If I still have the energy left, I want to check the Australian-to-US Exchange Rate later on - $118AU!!!

Actually, the RBC883 is only AU$79.95 ~= US$67.70.

I read in the product specifications that it charges at 250 mA per channel.

 

[TakeTheActive]

Re: New NiMH batteries (twice used) not charging anymore.

Actually, the RBC883 is only AU$79.95 ~= US$67.70...

Silly me!

I CLICKed on the top Charger LINK on the page for the LINK given and read all about the RBC889 ReZAP Pro instead of the RBC883 ReZAP Battery Doctor.

250mA MAX! Time for a new (0.5-1.0C) charger...

 

[squirrel]

Re: New NiMH batteries (twice used) not charging anymore.

for a jumpstart, paper clip across 2 cells, 1 good 1 bad, while in charger will jump the bad cell enough.

 

[TakeTheActive]

Re: New NiMH batteries (twice used) not charging anymore.

for a jumpstart, paper clip across 2 cells, 1 good 1 bad, while in charger will jump the bad cell enough.

Ah, the "NLee the Engineer" Method!

Personally, I'd do it OUT of the charger, just to be safe... :thinking:

 

[Gazoola]

Re: New NiMH batteries (twice used) not charging anymore.

[*][/list]A few seconds at OVER ~1.5-2.0VDC isn't going to matter a bit. You can safely charge an empty cell @ 4.0C (15-Minute Chargers) *UNTIL* heat begins to build (~70% SOC). A few seconds @ 3.7VDC is nothing. Plus, since the current available is so low (355mA), the output voltage of that adapter probably dropped anyway.

Great, I'll keep the DC adapter option in mind if it ever happens again and I don't have a spare charged cell lying around (not likely).

When I mentioned I was "talking" to a fellow is Australia, she came up with a slew of questions:

1. How hot is it there today?
   .
2. How far are you from Steve Irwin's zoo?
   (i.e. where are you? IIRC, isn't the zoo in Queensland?)
   .
3. Is the zoo still open?

Thanks!

:laughing:
Well it's cool here at the moment with winter on the way, 21 Celsius.
I haven't been to his zoo, it's 4,800 km from me! I did drive past it once when I toured Queensland, but I've seen enough Australian wildlife as it is, so didn't drop in. It is still running despite Steve biting the dust.

I CLICKed on the top Charger LINK on the page [...] and read all about the RBC889 ReZAP Pro instead of the RBC883 ReZAP Battery Doctor.

250mA MAX! Time for a new (0.5-1.0C) charger...

The RBC883 works great. It charges all the different sizes (A,AA,C,D,9v and 6V lantern) I have read a few posts about it not being able to charge high capacity batteries, but I havn't had any problems in that regard and have charged these batteries:
Powertech 2000mAh
Canon 2300mAh
Varta 2100mAh
Varta 2500mAh

The RBC883 Rezap can charge up to 4000mAh, and on my device itself, (about 2 yrs old), it says :
"Hi-capacity (over 2200mAH) AA NiMH batteries should be recharged on the upper contact position.", this is where the C,D cells charge

The charging current is 250mA variable. I suppose that variable means it is intelligently adjusted for the battery and state of charge.

I have used it for recharging standard alkalines including 9v batteries. This has been hit and miss in that some battery brands showed leaking some weeks later, while others gave only 3-5 top up charges. I just see the alkaline charging as an added bonus and not something that I have relied on.

All round the Rezap is excellent because of it's versatility, built in 'intelligence', and gentle charging which should ensure that you get good life out of your batteries. I know there are proponents of 1C charging, but there are just as many who say that slower gentle charge is better for any battery and yields better capacity. The caveat is that a quality charger is needed to charge at a gentle rate, to be able to detect the end of the charge properly, which I think the Rezap is.