Volts or mAh...which is more important?

As you can tell from my subject, I am new at batteries and charging.
I am one of those that had the cheap charger and wondered why the batteries crap out after a few minutes.
As I am educating myself from this great forum, I ran out and bought the C9000 charger and am on the road to "recovery".
However, I do have a noob question reagrding volts/mAh.
Is it more important to match your batteries according to their charged volts or mAh?
My quess is mAh?
Even if you have two identical brand batteries rated at i.e. 2000maAh, one could have charged at 1900m, the other at 1500m. Am I correct in thinking that these two (althought they can be used together) shouldn't?
In other words, should you match batteries at their charged mAh rating rather than their brands?
I know that a set of 4 brand new batteries will have pretty much the same ratings when charged, but I am asking about older batteries or even the semi-new batteries that show different mAh ratings.
Hope I am wording this correctly?

In your example (NiMh AA cells) matching/pairing by charged mAh would be advisable.

Assuming both cells discharge evenly in a 2xAA config, there would be less of a chance of getting into a reverse charge situation if the cells are matched by mAh.

I group based on capacity (mAh). I also dedicate sets of cells to a particular device vs. using a set of cells in different devices.

You can run into cell reversal if one cell in a multi-cell application completely discharges while the others continue to drain.

Voltage doesn't measure capacity. Also, the resting voltage will drop after removed from the charger. To test, note the cell voltages in the C9000 at the end of charge. Remove the cells and let them sit overnight, then test them with a multimeter. eneloop cells, in my experience, tend to have less of a resting voltage drop after charge than other NiMH cells. Even after sitting overnight, most of my cells only have a variance of .02V. But I don't use this to group my cells, rather just to get an idea of their resting voltage.

I also use a ZTS battery tester that uses a pulse-load to determine the approximate charge of the cell (this does not measure capacity). I use this more as a tool for pairing Lithium Primary cells that have been sitting unused for long periods of time, but I use it for NiMH and Alkaline cells as well.

For Li-Ion cells, I rely on voltage to pair as I don't own an analyzer for Li-Ion cells. The Li-Ion cells I use are protected and thus if one drains more than another, the cell is cut off by the protection circuit. NiMH cells are not protected, which is why grouping them based on capacity is important in multi-cell applications.

Another thing to note is uneven drain of cells in a given device. Take one of my Canon cameras for example. I've noticed that, after use, cells 2 and 3 drain faster than 1 and 4. It could be that it uses the middle cells to charge the internal backup battery, but I'm not sure. To help even things out, I move cells rotate cells 2 and 3 to the 1 and 4 positions after each charge.

A member of this forum has a good rule of thumb for NiMH cells: Once it's reached 80% of its rated capacity, it's pitched.

Finally, running your cells through periodic refresh/analyze modes can help to even out cells that may be draining unevenly. I try to do this for cells in storage once every 2-3 mo.

looking at the experience of a colleague: I use Sanyos, have done for several years. He recently bought some Energizer 2700s. The run time differences in his fenix between three sets of two batteries (vartas, the Energizers and another set) is significant. One drops after 10 minutes to lower output, another is good for 40 minutes, then pretty much dies. Just because it says 2700 doesn't mean that it supplies 2700.

So, test it, charge them individually, and if they don't last as well as you think they should, maybe check the voltage and then group differently.

Bret

if You do check and then pair cells together
and when Your charger can do this,
dont decide by the charged value, because it is nearly BS,
use the number gotten from discharging them, thats what coults for You



(+ give another try after a week or so of non charging, some cells tend to give high loss, for whatever reason)

Chase2b said:

As you can tell from my subject, I am new at batteries and charging.
I am one of those that had the cheap charger and wondered why the batteries crap out after a few minutes.
As I am educating myself from this great forum, I ran out and bought the C9000 charger and am on the road to "recovery".

Click to expand...

Excellent question, Chase2b. I'm in your position as well. I think that we should form a support group. We could call it the Fellowship of the Battered Cells. Perhaps Silverfox could develop a 12-step program for us? If we get less than 80% we would be discarded. But if we pass, maybe CPF would give us a C9000 full of Eneloops as a graduation gift?

Unless you know the batteries are from the same manufacturer the internal resistance can vary even though the voltage and mah could be identical and under varying loads they could discharge at a different rate than the others causing the runtime to vary and possible higher chance of overdischarging.

coppertrail said:

I also use a ZTS battery tester that uses a pulse-load to determine the approximate charge of the cell (this does not measure capacity). I use this more as a tool for pairing Lithium Primary cells that have been sitting unused for long periods of time, but I use it for NiMH and Alkaline cells as well.


A.

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Tha poses another question, if you don't mind...
I have a very good multi meter and have been reading about the ZTS, especially the MBT-1 tester.
I know that the ZTS puts a load on the battery but when it comes to trying to match cells, but wouldn't using a multi meter on the MA setting give you a good indication of battery life? Especially a digital read-out meter (like mine) instead of LED's as is on the ZTS?

A multimeter mA setting reads current, not capacity. The only way to know the capacity of a cell is to do a discharge test on something like the Maha C-9000 or LaCrosse BC-900. Only then can you match like pairs.

Marduke said:

A multimeter mA setting reads current, not capacity. The only way to know the capacity of a cell is to do a discharge test on something like the Maha C-9000 or LaCrosse BC-900. Only then can you match like pairs.

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Okay, got it. But isn't matching the current (ma) via a multi meter still an indication of the "life" or at least for matching?

Chase2b said:

Okay, got it. But isn't matching the current (ma) via a multi meter still an indication of the "life" or at least for matching?

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You cannot measure a cell like that. Current measures how much juice is flowing in our out of the cell, or through the LED. This is primarily a function of the device in use, not the cells it is using.


Using the mA setting of the multimeter and trying to measure a cell will just short circuit the cell, which generally leads to bad things...


The ONLY way to know capacity is to conduct a discharge test by emptying the cell under a known load and integrating the energy consumed. This can be done automatically using one of the better battery chargers, such as the C9000 or BC-900. It's a very useful feature to have for the $35 it costs.

Chase2b said:

Okay, got it. But isn't matching the current (ma) via a multi meter still an indication of the "life" or at least for matching?

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I've got to reinforce what Marduke said in case you are ever tempted to try it. Do not ever connect a meter on the mA setting to a battery. This is a really bad thing to do that will do no good at all to the meter. Do not even be tempted.

Mr Happy said:

I've got to reinforce what Marduke said in case you are ever tempted to try it. Do not ever connect a meter on the mA setting to a battery. This is a really bad thing to do that will do no good at all to the meter. Do not even be tempted.

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What about internal resistance? Can you use a DMM to measure the resistance within a cell? If you measure and record the resistance of new cells, would you be able to compare it to a measurement made a year later to see if the resistance is increasing?

You must never connect a meter on the resistance setting to a battery either. In fact, never connect a meter on the resistance setting to an energized circuit.

You can measure the internal resistance of a battery, but you have to make voltage and current measurements and calculate the resistance indirectly. There are other posts here that explain the procedure. They should turn up in a search for "internal resistance" (I think -- I have not tried that search).

Mr Happy said:

You must never connect a meter on the resistance setting to a battery either. In fact, never connect a meter on the resistance setting to an energized circuit.

You can measure the internal resistance of a battery, but you have to make voltage and current measurements and calculate the resistance indirectly. There are other posts here that explain the procedure. They should turn up in a search for "internal resistance" (I think -- I have not tried that search).

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Will do that search right now! Thanks for pointing me in the right direction, Mr Happy!

Marduke said:

You cannot measure a cell like that. Current measures how much juice is flowing in our out of the cell, or through the LED. This is primarily a function of the device in use, not the cells it is using.


Using the mA setting of the multimeter and trying to measure a cell will just short circuit the cell, which generally leads to bad things...


The ONLY way to know capacity is to conduct a discharge test by emptying the cell under a known load and integrating the energy consumed. This can be done automatically using one of the better battery chargers, such as the C9000 or BC-900. It's a very useful feature to have for the $35 it costs.

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I apologize if I'm not being clear in my questions. I understnad about the C9000 showing capacity in the cells. In fact I just had a set do its first discharge and it gave the mAh data.
On my multimeter, in the VDC area, I have ranges of 20, 200,600, but also there is a range for 200m and 2000m. That is what I am questioning. Is that the milliamps rating? And can you use THAT reading to determine the matching of cells?

Chase2b said:

I apologize if I'm not being clear in my questions. I understnad about the C9000 showing capacity in the cells. In fact I just had a set do its first discharge and it gave the mAh data.
On my multimeter, in the VDC area, I have ranges of 20, 200,600, but also there is a range for 200m and 2000m. That is what I am questioning. Is that the milliamps rating? And can you use THAT reading to determine the matching of cells?

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And in case our previous answers were not clear, I'll follow up with another resounding NO! Your meter can only measure current, NOT capacity. The ONLY way to pair cells of like capacity is to discharge them, find their true capacity, and pair them up.

Chase2b said:

I apologize if I'm not being clear in my questions. I understnad about the C9000 showing capacity in the cells. In fact I just had a set do its first discharge and it gave the mAh data.
On my multimeter, in the VDC area, I have ranges of 20, 200,600, but also there is a range for 200m and 2000m. That is what I am questioning. Is that the milliamps rating? And can you use THAT reading to determine the matching of cells?

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Your questions are very clear, and so are the answers.

Perhaps what is confusing you is the difference between milliamps (mA) and milliamp-hours (mAh). The first, mA, is instantaneous current. This is what your meter can measure. The second, mAh, is accumulated charge or capacity, which is what the C9000 can measure. You get the charge in mAh by taking a small current from the battery and adding it up over a long period of several hours until the battery is drained. The final total is the capacity, measured as milliamps times hours. The "long period of several hours" is an unavoidable part of the measurement procedure. There is no shortcut.

Marduke said:

And in case our previous answers were not clear, I'll follow up with another resounding NO! Your meter can only measure current, NOT capacity. The ONLY way to pair cells of like capacity is to discharge them, find their true capacity, and pair them up.

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Believe me I understand exactly what you are saying. I am just confused about the milliamp ratings. Isn't the M reading the amount of current being put out? If two cells have about the same ma (current)rating (according to the meter) then are they not "matched" CURRENT WISE.
I know you can have a rated 2000mah (discharged= 1900) and another rated 2000mah (discharged= 1500) and they are NOT matched. But for argument sake they both have a 1500 (charged)milliamp rating. If they are both putting out the same amount of current isn't that "good".
Consequently can it go the other way too.
i.e. 2 exactly charged mah readouts of 1900 and one has a milliamp rating of 1500 and the other 1350.

Note: I am not suggesting that the milliamp rating and the mah ratings are supposed to be the same...

Since I am a novice, I am just trying to understand what the meter is telling me.
Also trying to decide if I need a ZTS tester or just use a meter. (I know the ZTS put a load on it).

I'd suspect it was millivolts.
As far as the current being supplied is concerned... I'm going to try and explain it how I see it, it may be wrong!

let's take a fictional pair of batteries. We'll call them George and John.

Both start off fresh; George is labeled 2700 and so is John.
John gets a knock at some point and starts deteriorating.
Now, unless you've tested it... how are you going to know?

for example. 1A load, 2700mAh --> 2.7 /1 should mean 2.7h IF the battery gets drained to 0 (which is not good). It might be that John charges great but can't hold the charge and discharges faster due to lower internal resistance - he becomes more of a sprinter, where George is a marathon runner. It may be he still has the same capacity, but because of the chemical changes (also caused by use), it's not necessarily deliverable in the same way. You may never see this in normal use because the two would complement each other. Yes, IMO, it would be desirable that they would both have a similar current delivery curve to make sure one's not trying to compensate for the other without delivering current to the application.

Without testing and / or conditioning and careful checking, you may get and issue.
On the other hand, I've not discharged a set of NiMH in anger for a looong time (probably close on six years now) and I don't have issues; but then they get used in my flash and the ones that didn't get charged / discharged really did get memory and are now used for other things. They get replaced once every year or two, two sets of four at a time.

hope this helps.

Bret