Reviving "Old" Ni-MH Cells?

[IonicBond]

One can also try the Maha Powerex MH-C401FS.

Designed back in the day when cell resistance was higher than now, and it had special pulse / negative pulse charging algo's.

Use the FAST position, not slow (cell capacities were much lower and it is easier to miss the termination with too low of a current level). Cells will get HOT. Keep an eye on them, and don't charge them on your couch.

This used to be the "goto" charger decades ago well before the C9000, and I normally don't recommend it for daily use. But I'll run my cell through them once in a blue moon. Followed by a discharge and recharge in a more modern charger.

That seemed to help revive some older cells, but not near new capacity. Still, it was an interesting result when the normal charger cycling didn't seem to improve any.

It would make a great test subject to see the benefit from using it once in a awhile. Again - I wouldn't use for daily use these days, but a good tool for any battery-geek toolbox.

 

[IonicBond]

The more modern option:

Use a charger that has a 1C charge rate capability. If they aren't so high-resistance to be rejected by the charger, use the 1C option, ie 2A for a 2000mah cell.

Super long storage may make them resistant to becoming "vibrant" as SilverFox noted many years ago - even with repetetive low current charge cycles. Basically, they won't accept or deliver anything but a superficial surface charge. You need a higher current to force a deeper charge to get them vibrant again, whereupon you can resume normal charge rates. (0.5 to 1C)

Yes, they will get hot to the touch. Hot enough that you can barely hold your finger on them. That's different than *burning your finger*. But successive 1C recharges should make them go cooler each time - unless the battery is just plain unrecoverable.

Many nimh batteries are babied to death right from the start, walking themselves down over time with weak current recharging.

No need to go overboard, but every once in awhile, be sure to treat an nimh to a 1C charge to keep them healthy.

 

[WalkIntoTheLight]

Super long storage may make them resistant to becoming "vibrant" as SilverFox noted many years ago - even with repetetive low current charge cycles. Basically, they won't accept or deliver anything but a superficial surface charge. You need a higher current to force a deeper charge to get them vibrant again, whereupon you can resume normal charge rates. (0.5 to 1C)

Yes, they will get hot to the touch. Hot enough that you can barely hold your finger on them. That's different than *burning your finger*. But successive 1C recharges should make them go cooler each time - unless the battery is just plain unrecoverable.

I have never heard that. I'm not sure what to make of it. But, I've got a couple of NiMH cells sitting around that I haven't got around to recycling. They are so bad they won't even accept a slow charge, except to bring up their resting voltage to 1.4v. But as soon as I apply any modest discharge to them, they almost immediately die.

So, I'll give it a shot. I'll force-feed them a current that I think will just cause them to overheat. But, maybe your way will work? I'll find out...

 

[mcm308]

Zapping with a 12V car battery does work on dead zero volt batteries. Its works and I have done it. You could probably zap yours too and see if it makes a difference. It'll cook any crystals that have formed.

I forget what its called but what happens is crystals start to form inside the cell ultimately shorting them out from the negative to positive side.. When you zap them with a 12V car battery, it like vaporizes the crystals and the batteries can be returned to service like new.

Only do it for a second or two. Let them sit and charge em up. See what you got. Nothing to lose..

 

[WalkIntoTheLight]

Follow up...

I tried charging at a fast 1C rate. No difference from charging at a slow rate. The end result is that the batteries will only take a surface charge, and when I use them they can only provide low discharge rates for a short period of time. (For example, they'll light up a 1xAA light at ~20 lumens for a few minutes.)

So, at least for my worn-out cells, fast-charging doesn't revive them.

Next, I'll try zapping with a 12v battery. I don't expect it will work, but why not give it a try!

 

[WalkIntoTheLight]

Zapping with a 12V car battery does work on dead zero volt batteries. Its works and I have done it. You could probably zap yours too and see if it makes a difference. It'll cook any crystals that have formed.

I forget what its called but what happens is crystals start to form inside the cell ultimately shorting them out from the negative to positive side.. When you zap them with a 12V car battery, it like vaporizes the crystals and the batteries can be returned to service like new.

Only do it for a second or two. Let them sit and charge em up. See what you got. Nothing to lose..

Follow up...

As expected, that didn't work on my old worn-out NiMH cell. All it did was warm up my cell a bit. But after a rest, the charge/discharge characteristics didn't change. It only accepts a surface charge.

IIRC, the 12v zap trick used to be mentioned way back in the days of NiCad batteries. I've never heard it recommended for NiMH. In any case, it doesn't appear to work.

IMO, once a cell is old and worn-out, there's no reviving it.

 

[mcm308]

Follow up...

As expected, that didn't work on my old worn-out NiMH cell. All it did was warm up my cell a bit. But after a rest, the charge/discharge characteristics didn't change. It only accepts a surface charge.

IIRC, the 12v zap trick used to be mentioned way back in the days of NiCad batteries. I've never heard it recommended for NiMH. In any case, it doesn't appear to work.

IMO, once a cell is old and worn-out, there's no reviving it.

Yea, the zap trick is good for when the battery is at zero volts and wont take any charge. Wasnt sure if it would work on batts that already have voltage. Was worth a shot I suppose..

 

[PartyPete]

I've had a few instances where the battery is essentially dead and the Eneloop charger and my smart chargers will show and error and not charge it.

I use an old Rayovac dumb charger to revive them so to speak and that way the good chargers will actually recognize and charge them.

 

[apagogeas]

Well, really old batteries probably don't worth the trouble even if the internal resistance is not so elevated. I have some quite old (more than 10 years old) Kodak of various labeled capacities (one at 2100 and several at 2500mAh). I have tested a couple of them and their IR is around 200-300mΩ or so which is rather good I can say for their age. I apply a 500mA CC discharge (Liitokala 500) and they do return 1800mAh (the 2100 one) and 2000-2100mAh most of the 2500 version which is very impressive too. However, the self discharge is huge, in less than 2 weeks all of them get empty down to 0.8V. They also get around 3500mAh to get charged which means quite a lot of charge is consumed internally to losses (500mA CC charge). So not really worthy for demanding tasks and in low drain devices it is a burden as I did try to use them in a mouse but I got bored of charging them so regularly. I keep them around, just curious how long it will take to have their IR skyrocket.

 

[magellan]

Very informative thread, all.

I just have one of these batteries, a Sanyo 2500, pictured below.

http://imgbox.com/lTsJA8qY

I don't know exactly how old it is, but I knew it was old. It's still useable, but it takes hours longer to charge in my Opus BT-C2000 charger than my other, newer batteries like my Eneloops and Amazon labeled types.

The charge never seems to terminate, which I chalked up to high internal resistance (I always stop it when the display shows as having put 4500 or 5000 mAh hours into the battery). I should let it run overnight sometime and see if it would actually terminate at some point.

It also seems to get noticeably hotter to the touch while charging than the other newer batteries, which again, I attributed to the higher internal resistance (I'm assuming that greater resistance means more energy dissipated as heat).

 

[WalkIntoTheLight]

I don't know exactly how old it is, but I knew it was old. It's still useable, but it takes hours longer to charge in my Opus BT-C2000 charger than my other, newer batteries like my Eneloops and Amazon labeled types.

The charge never seems to terminate, which I chalked up to high internal resistance (I always stop it when the display shows as having put 4500 or 5000 mAh hours into the battery). I should let it run overnight sometime and see if it would actually terminate at some point.

Older cells can often not give strong -dV/dt signals. That is what your charger is likely looking for, and it misses it so never terminates. Some chargers will eventually stop when a certain voltage is reached, or even after a certain time period has elapsed. I'm not sure if your charger has those backup methods. Probably not, if you've dumped 5000mAh into it and it still hasn't terminated.

But it's possible that it just hasn't reached full charge, yet. On really old cells, I usually have to dump in twice their capacity (as measured by a discharge test) in order to fully charge them. It probably won't hurt them much by letting it run overnight to see. They're crap cells anyway, so they probably deserve a bit of abuse.

 

[magellan]

Older cells can often not give strong -dV/dt signals.

Ahh, could be something like that. I might let it run overnight and see what happens.

I can actually get a couple of weeks general use out of it, running it in a Fenix E99 Ti AAA light, which has a low, medium, and high. I sort of like the idea of getting some benefit from such an old cell. ;-)

They're crap cells anyway, so they probably deserve a bit of abuse.

LOL

I'm someone who pretty much babies their batteries. All the knowledge I gained here about battery usage for lithium ions, NiMH, or whatever has apparently percolated deep into my aging brain and I am probably a little too obsessive-compulsive in following all the big and little do's and don't's. ;-)

 

[magellan]

I searched and found this thread from 2006. Mine is also an HR 3U 2500.

http://www.candlepowerforums.com/vb/showthread.php?109138-Sanyo-HR-3U-2500mAh-vs-Energizer-2500mAh