When.. to charge Sanyo Eneloops?

I have Sanyo's AA/AAA batteries. Often they're lying around and I forget if they're charged or not. I use a digital VOM and assume they're fully charged if they register in the 1.3x range. Is this range feasible to say they don't require charging? Is the voltage different for AA and AAA?

I have the Maha C9000 charger

What VOM range would you allow them to drop to before a recharge? In advance thanks..

I cycle mine every few months. Granted that they will store a year at 85% but I get bored waiting for my eneloops to discharge.

Seriously, 1.3 volts is over 75 percent. The top voltage drops off pretty fast then it holds steady for a long time.

radunn said:

What VOM range would you allow them to drop to before a recharge?

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I tried to figure this out a while back too and found a post from CPF's "Mr. Happy" that said (roughly) this:

Resting Voltage versus charge:

1.20V == 0% charge
1.33 - 1.42 == 100% charge

This is rough and by no means completely reliable. With Eneloops it seems close-ish.

I've had one cell act strangely, reading 1.28V over and over for weeks when I'd test it, and then one day it just died. I found it resting at about 1.21V and when I ran a discharge on it, it dropped to 0.9V almost instantly.

Maybe use the above as a rough guide and if you want, do a very short discharge at 500 mA on cells you wonder about. Look at their Voltage under load. Cells with a lot of life won't pull down under 1.20 V under load. When they dip below 1.20V I think they are in the last 1/3 of their run time. Or run some full discharges and develop your own metrics for what resting Voltages and what loaded Voltages correspond to what charge levels on your own cells.

NiMh is really cool stuff, but the state of charge is a very difficult thing to quantify.

Brian.

blgentry said:

I tried to figure this out a while back too and found a post from CPF's "Mr. Happy" that said (roughly) this:

Resting Voltage versus charge:

1.20V == 0% charge
1.33 - 1.42 == 100% charge

This is rough and by no means completely reliable. With Eneloops it seems close-ish.

I've had one cell act strangely, reading 1.28V over and over for weeks when I'd test it, and then one day it just died. I found it resting at about 1.21V and when I ran a discharge on it, it dropped to 0.9V almost instantly.

Maybe use the above as a rough guide and if you want, do a very short discharge at 500 mA on cells you wonder about. Look at their Voltage under load. Cells with a lot of life won't pull down under 1.20 V under load. When they dip below 1.20V I think they are in the last 1/3 of their run time. Or run some full discharges and develop your own metrics for what resting Voltages and what loaded Voltages correspond to what charge levels on your own cells.

NiMh is really cool stuff, but the state of charge is a very difficult thing to quantify.

Brian.

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That's not right. 0.9V == 0%

1.2v resting is usually pretty much discharged.

mccririck said:

That's not right. 0.9V == 0%

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If you attempt to discharge a cell registering 1.2v resting, it will very quickly drop to .9 so there is little to nothing left in it.

I use 1.37+ = Full
1.25-1.27 = 50%
1.2 dead

This is pretty close for resting voltage for Eneloops.

Upon reading the original post I found a pair of partially discharged AA Eneloops in my battery box and stuck them in the charger. They started out at 1.36 volts on the VOM. My charger is a LaCrosse BC-700 which allows display of voltage, and accumulated charge (mAh) as the batteries are charging. I recorded these values at random times as the batteries were charging. Results:

Voltage Charge
------- ------
1.36 V 0 mAh (start)
1.42 V 599 mAh
1.46 V 710 mAh
1.48 V 749 mAh
1.52 V 1015 mAh
1.50 V 1027 mAh (charge complete)

I don't think the charger has any way of accounting for efficiency of charge (losses to heat, etc.) but the batteries do not get warm until almost fully charged. So I suspect heat losses are small until around 1.50 V. With this assumption, and given a rated capacity of 2000 mAh, a reading of 1.35 V no load on a VOM means the battery is around half-charged.

Of course a battery that reads a certain voltage under load will deliver quite a bit less voltage with a load. Since you own a voltmeter I assume you may be adept with a soldering iron. You can get a holder for a single AA battery and connect it up to a resistor that will approximate the load corresponding to your flashlight of choice. It'll be a rough approximation but much more realistic than testing with no load.

You'll get more meaningful results checking Ni-mh batteries under load.

Norm

dgbrookman said:

Upon reading the original post I found a pair of partially discharged AA Eneloops in my battery box and stuck them in the charger. They started out at 1.36 volts on the VOM. My charger is a LaCrosse BC-700 which allows display of voltage, and accumulated charge (mAh) as the batteries are charging. I recorded these values at random times as the batteries were charging. Results:

Voltage Charge
------- ------
1.36 V 0 mAh (start)
1.42 V 599 mAh
1.46 V 710 mAh
1.48 V 749 mAh
1.52 V 1015 mAh
1.50 V 1027 mAh (charge complete)

I don't think the charger has any way of accounting for efficiency of charge (losses to heat, etc.) but the batteries do not get warm until almost fully charged. So I suspect heat losses are small until around 1.50 V. With this assumption, and given a rated capacity of 2000 mAh, a reading of 1.35 V no load on a VOM means the battery is around half-charged.

Of course a battery that reads a certain voltage under load will deliver quite a bit less voltage with a load. Since you own a voltmeter I assume you may be adept with a soldering iron. You can get a holder for a single AA battery and connect it up to a resistor that will approximate the load corresponding to your flashlight of choice. It'll be a rough approximation but much more realistic than testing with no load.

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The problem with your testing is your voltage numbers are while there is a charge current given to the cell. The discussion is a cell with no load and "resting". And at 1.35V resting you have a very close to 100% charged cell. Check that battery that was 1.5V the next day on a volt meter sitting and not in charger and you will see considerably less voltage.

I offer you quote from Zebra light's sc52 specs:

"Low battery alert when the light is*switched*Off with AA batteries (LED flashes every 80 seconds if the battery voltage is below 1.06V)"

..is 1.06 where the Zebra thinks it has just run out of useable juice? or is it more f a warning to remind you to recharge and not allow over discharge? I think most probably the latter, with 1.2v being close to 'depleted without damage.'

TedTheLed said:

I offer you quote from Zebra light's sc52 specs:

"Low battery alert when the light is*switched*Off with AA batteries (LED flashes every 80 seconds if the battery voltage is below 1.06V)"

..is 1.06 where the Zebra thinks it has just run out of useable juice? or is it more f a warning to remind you to recharge and not allow over discharge? I think most probably the latter, with 1.2v being close to 'depleted without damage.'

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That number also is likely with a load on it. You'd have to see when it hits warning, pull the battery and check on voltmeter while resting to get a resting comparison. My guess is around 1.21-1.22V resting but it depends much on the amount of load also.

lwknight said:

I cycle mine every few months. Granted that they will store a year at 85% but I get bored waiting for my eneloops to discharge.

.

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as almost the opposite of that . . .

I did not cycle some, and they were in serious need of a few full cycles.
A group of my AA eneloops (originals), were charged and parked for about a year or more, while they still would operate something, I could tell that they were in great need of cycling. On various testing a significant ammount of thier still usable capacity was weak. Even after a recharge.

For example at a 1amp type discharge they could not hold voltage for long (about 700-900ma to .9v). I even changed the parameters on the hobby charger (.5A .1v discharge) to account for thier Rip Van Winkleism
I singularly deep discharged them (slow and below 1v) and it took a few cycles to get them back up to reliable and normal for them.
They are now happy, but wish someone would use more of them, more often.

So even though they can do more than a year hang time, I still will discharge and refresh all the chemicals as maintance.
It was not just about capacity and voltage but how vibrant it still was (or whatever technical term that would be) and resistance and all.

I am not going to put up all the stats on them, because A) I never intended to let them sit there. B) I dont use any one discharge method or charger C) there is a lot of them .

I suspect that the OP is probably more aware of and uses his more than these were, and therfore does not have such issues. I am indicating that still "Holding A Charge" or "Having Capacity still" or "Displaying A Voltage" does not equate to pumping that out quickly, and cycling has not dissapeared from rechargable society.

I also am also leaning my opinion on li-ion cycling, as most of them are doing better when used more often (all assuming that is done the way they like it).

If your going to test a battery using voltage, like others have said, put a load on it, or get a tester that uses a load, the voltage and testers that only use voltage have never proved to be a reliable measure.

Other things less related: Out of ~50 of these original eneloop cell items, both used and unused, 2 were unrecoverable, I suspect that they got reverse charged while used in 4x series in some device.

You mean Rumpelstiltskin-like behavior in that before they were straw and now they are gold? Or maybe mixed up the German with the Grimm tale of Rip Van Winkle ? (the one who slept a long time)

What is the lowest number a good battery goes down to under load? 1volt? and a depleted good battery? .9? .8 ?

will test myself later, after the sun comes up...but be my guest..

TedTheLed said:

You mean Rumpelstiltskin-like behavior in that before they were straw and now they are gold? Or maybe mixed up the German with the Grimm tale of Rip Van Winkle ? (the one who slept a long time) ..

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thats the one, I feex it.
When I was waking them up thoughts of passivation layer were dancing in my head (whatever a passivation layer is Ya know, that it did it on purpose or by design.

TedTheLed said:

What is the lowest number a good battery goes down to under load? 1volt? and a depleted good battery? .9? .8 ?

will test myself later, after the sun comes up...but be my guest..

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I think that the 1.2V kind of battery should be able to hold the 1V under the normal load it would be used for. relative, like if it is one of those 1600ma high output kind it should hold at least the 1V under a high load still.

My expectation for the eneloop 2000mah thing is at 1amp (.5C) it holds the 1+V output for most of its discharge, that is not asking too much is it?

The charger was set to the standard .9V for the cutoff, when I noticed that it cutout way to early, but there are wire leads to the battery, tiny bits of resistance. I have speaker wire leads of short length but there is still a small voltage drop there. Then of course one hobby charger gives quite different results. My better voltmeter decided to quit working properly, so about all i can do is compare the batts and how they should act on the hobby charger they are on at the time.

I got some of the newer 2nd generation eneloops , and can use them to compare also, but my facts are few, a man with many chargers never knows what miliamps it is .
The maha charger (808style) slightly undercharges, and has 2 different speeds (soft charging). I prefer not to use the hobby charger for charging because it uses "overcharge" for the v-drop for terminations, and the "slow" charger stops at 2000ma. Did the battery get "topped-off" or not, does that charger even top them off. Then temperatures in the house are fluxuating wildly daily, from 74*F to as low as 56*F at night. Add to all of that the rate of charge can effect slightly the "forming" so a faster charge without cooking it can gain a faster discharge rate. All to many variables to do anything more than "feel it out" and get a good idea of what is going on.

TedTheLed said:

What is the lowest number a good battery goes down to under load? 1volt? and a depleted good battery? .9? .8 ?

will test myself later, after the sun comes up...but be my guest..

Click to expand...

A simple testing:
2 new second generation 2000ma eneloops (1500x)
1 re-charge out of package no cycling
1A discharge to .9V cutoff
did about 1700-1800mah , at least .95-1V for most of that (when i was looking)

That is just fine with me, enough to rely on through any job, in all the stuff I use them in.
Then go back to what I was saying about the parked originals, it did about 1/2 that, that is why I felt a great need to cycle them.
Even when I put the parked ones on my (home made) incan bulb discharger thing, the output was visually weak (compared to my expectation)

..and how long did it take ? 1.7 - 1.8+ hours I guess at 1 amp to deplete, right? and what was your starting voltage? seems 1.06v is a reasonable resting warning point, meaning about half depleted it would seem, more or less..

TedTheLed said:

..and how long did it take ? 1.7 - 1.8+ hours I guess at 1 amp to deplete, right? and what was your starting voltage? seems 1.06v is a reasonable resting warning point, meaning about half depleted it would seem, more or less..

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I dont really pay that much attention to it, the hobby charger beeps loudly when done, and i dont nessisarily care at the time. There is also a bunch of accuevolution AAs that I am cycling, batteries everywhere , and i am doing other work.

the unloaded voltages can be all over the place from ~1.3- to 1.4+ all depending on how long ago it was charged, and just normal variations.
Take this from above what

Mr. Happy wrote
1.20V == 0% charge
1.33 - 1.42 == 100% charge
I get pretty much the same results as low as ~1.29 reading on a fully charged. I really thought that Mr. Happy was indicating that we know nothing from all of that, except if it is empty, and even then, they can float back up some in voltage as the weak chemicals can output slowly. Example: a weak and discharged battery could show as high as Unloaded 1.37v and not be able to run a flashlight good for a few minutes.
So for unloaded voltages , a guess would be as usefull.

If i extrapolate on what Mr Happy wrote, i would write it like this
~0v - ~1.2V = 0% might have been reverse charged (in series) to Probably empty.
~1.29 - ~1.47 = in that entire volt range any one of them could be 10% to 100% charged mabey
and depending on many factors

Loaded (discharging)
The 1 amp loaded voltages on some fully charged Originals, give it a few seconds to stabelise I get just holding 1.0v to highs of holding 1.3+v at the First of the discharge. all over the board again, some of that due to different ones cycled different ammounts and ways.

Then take the discharge graphs we have for the ni-?? batts and the flat graph line for normal discharges. The tendancy is that it Holds the voltage fairly steady (through the viable capacity of the cell) , add in the variations in discharge voltages (that stay quite the same for each battery) different forming rates, freshness of cycling.

I can Not believe that even with a load and voltage reading, or wizz bang tester, that a person could factually know anything about the state of charge , of someone elses batteries. Impedance and resistance testing could show the overall usefullness of the cell (for loads) , which might be more valuable than just the charge state.
Unless
Using the same method of charge, the same number of cycles, using a set as a team, and having a matched set, mabey then a person could assume how much capacity is left (with a load and voltage reading)? Knowing how that set reacts, specific to how they are using it.

I donno what do you think? because I dont usually have to care. Usually I just Re-Top them off, change them often, and have them Tested to insure they will "do the job" and they always have.

I can use the voltage on my Eneloops (measured with a DMM) as a fairly reliable indicator of their state of charge.

When they are freshly charged the voltage is somewhere around 1.4 V, maybe down to 1.38 V after a month or two.

As they sit, the voltage drops until after about a year they might be at 1.33 V or so. I can use this to tell the difference between "long ago" charged Eneloops and freshly charged Eneloops.

Now if you leave fully charged Eneloops to sit on the shelf for several months they can develop a temporary lack of vibrancy, seen as a bigger drop in voltage under load and an apparent weakness in high power applications. This temporary weakness can be recovered and full vibrancy restored by cycling the cell once or twice, or maybe doing a break-in cycle on the C9000.

The lesson here is that NiMH cells like to be used, they don't like to sit around.

As for discharged cells, a resting voltage of 1.20 indicates a completely empty cell. If you try to put any load on the cell at all the voltage will drop rapidly and no power will be delivered. This is why a controlled discharge is stopped at a voltage of about 0.9 V. As soon as you stop the discharge the voltage should rebound to about 1.2 V and sit there.

Mr Happy said:

I can use the voltage on my Eneloops (measured with a DMM) as a fairly reliable indicator of their state of charge.

When they are freshly charged the voltage is somewhere around 1.4 V, maybe down to 1.38 V after a month or two.

As they sit, the voltage drops until after about a year they might be at 1.33 V or so. .

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Ok i get it you can get a good idea of how long they have been sitting around.

Re-Reading i see that the OP (radunn) didnt say some of them were USED partly or not. Just if they had been charged and they are parked.

Meaning, how would a person tell the difference between a parked one, and a partly used one , if a parked one can display the same voltages as a partly used one, and be at 2 different states of charge. From my loose testing, I could not get a same voltage reading from 2 full charged, fully functional batts even
The new ones probably would give very similar results. But the cool thing about eneloops is they lasted.

Mr Happy said:

If you try to put any load on the cell at all the voltage will drop rapidly and no power will be delivered. This is why a controlled discharge is stopped at a voltage of about 0.9 V. .

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These ones that were really weak from being parked and old (originals , would be ~6 years old) a lot of the power could still come out of them at either a low rate, or a lower voltage. To get them to work again, i ran them (basically) all the way down, and recharged them again. I thought at first they might be finished/end-of-life/unusable but they were not.
If i relied only on the machine and only stopping at .9v , I did not think it would "full cycle" them, that is why I use many methods, and methods that are unconventional. After all nothing to lose

you take it lower than .9? if so how? does the recycling in a (which?) charger take it below .9? if so, how low?