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Thread: Volts or mAh...which is more important?

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    Default 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?

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    Flashaholic* Black Rose's Avatar
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    Default Re: Volts or mAh...which is more important?

    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.

  3. #3

    Default Re: Volts or mAh...which is more important?

    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.

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    Default Re: Volts or mAh...which is more important?

    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

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    Default

    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)

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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Chase2b View Post
    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".
    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?

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    Default Re: Volts or mAh...which is more important?

    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.
    Fenix Split rings 1400+ sent, SWIVELS now available also!
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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by coppertrail View Post
    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.
    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?

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    *Flashaholic* Marduke's Avatar
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    Default Re: Volts or mAh...which is more important?

    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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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Marduke View Post
    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.
    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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    *Flashaholic* Marduke's Avatar
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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Chase2b View Post
    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?

    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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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Chase2b View Post
    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?
    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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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Mr Happy View Post
    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.
    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?

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    Default Re: Volts or mAh...which is more important?

    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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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Mr Happy View Post
    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).
    Will do that search right now! Thanks for pointing me in the right direction, Mr Happy!

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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Marduke View Post
    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.
    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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    *Flashaholic* Marduke's Avatar
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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Chase2b View Post
    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?
    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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    *Flashaholic* Mr Happy's Avatar
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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Chase2b View Post
    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?
    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.
    Last edited by Mr Happy; 01-24-2009 at 01:15 PM.

  19. #19

    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Marduke View Post
    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.
    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).

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    Default Re: Volts or mAh...which is more important?

    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

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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Chase2b View Post
    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 think you still do not understand the difference between current and capacity.

    To put it simply and plainly, you cannot match "current". There is no such thing as "current matching". Cells do not have a "mA" rating, which is current. They have a "mAh" rating, which is capacity. Trying to measure the "current" of a cell with a multimeter doesn't give you a measure of ANYTHING, it just does one of 3 things (or some multiple thereof):

    1) blows the fuse of your multimeter
    2) blows the multimeter itself if it is unfused
    3) causes the cell to vent/explode because you are short circuiting it

    The ZTS puts a cell under load, and measures voltage.

    Since you have the Maha, why try to use the meter at all? You can test a cell's capacity, and match them accordingly for use in various devices. This only needs done infrequently to spot check cell health.

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    Default Re: Volts or mAh...which is more important?

    Quote Originally Posted by Chase2b View Post
    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".
    Dang! Had typed a response but must have hit "back" by mistake. Let me try again.

    If I understand correctly (being a newbie, it's quite possible that I don't) the case above does not show they both have a 1500 mAh rating. They both have at least a 1500 mAh rating, though. If you were to use these two cells in a device, the 1500 mAh cell would discharge first since it has less capacity. The 1900 mAh cell would still have available energy at this point. If you continue to use this, you could have a cell reversal. As the cells are connected in series, the + of one connects to the - of the other. As the one cell still has deliverable energy and the other doesn't, the one will start to charge the lower one. As they are connected in reverse to each other, the one gains a charge but a negative charge. By using matched cells, they both have close to the same capacity and they will both run out of energy close to the same time. This way, one cell cannot end up charging the lesser-capacity cell. Also, the device will last longer because you don't have one cell running empty quickly, resulting in the entire "group" of cells or "battery" of cells going below the minimum voltage required to power the device.

    The capacity of the cell can only be measured after draining it, to see how much energy it can deliver. I can take a 2000 mAh cell and put 2000 mAh into it (say .5C or 1000 mA for 2 hours), or I can put 3200 mAh into it (0.1C or 200 mA for 16 hours). The cell will only retain what it is capable of retaining. The extra energy will be lost to heat, but the cell can't retain it. The only way to actually tell how much it did retain is to drain it and measure the amount removed.

    Perhaps I'm stating the obvious or talking gibberish, just thinking out loud here and more asking a question than trying to state fact.

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    Default Re: Volts or mAh...which is more important?

    ...
    Last edited by fireguy; 01-25-2009 at 05:53 PM. Reason: Accidental duplicate post removed.

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    Exclamation A Basic Understanding of Electricity is MORE Important!

    Quote Originally Posted by Chase2b View Post
    I apologize if I'm not being clear in my questions... ...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?
    Pardon me for being blunt, but, IMHO, you are being VERY CLEAR in demonstrating your lack of knowledge in basic electronics and would benefit greatly from reading a few hours of theory.

    If you're in the VDC (Voltage Direct Current) area on your DMM, why would there be a selection for current? Current selections are in the ADC (Amps Direct Current) area; Resistance selections are in the OHM area. AC voltage selections are in the VAC (Voltage Alternating Current) area. Did you happen to read the DMM manual?

    I'm sorry but I get very concerned when someone is doing something (possibly dangerous) that they have no basic knowledge of. For example, I get very nervous watching folks giving advice to newbies on installing three-way switches that have no clue what Hot/Neutral/Ground means.

    Quote Originally Posted by Mr Happy View Post
    ...Perhaps what is confusing you is the difference between milliamps (mA) and milliamp-hours (mAh)...
    I STRONGLY disagree! IMO, what's confusing the OP is the difference between VOLTS and AMPS.

    He's not going to understand your answers until he understand the basics - i.e. he don't know the 'language' you're speaking yet...

    Quote Originally Posted by Chase2b View Post
    ... And can you use THAT reading to determine the matching of cells?
    NO! You can't even GET a capacity reading using your logic.

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    Thinking Where's the LOAD?

    Quote Originally Posted by Chase2b View Post
    ...But isn't matching the current (ma) via a multi meter still an indication of the "life" or at least for matching?
    Sure!

    The current THROUGH A LOAD (ma), measured via a multi meter can be an indication of the "life". But, I don't see where you mentioned the value of the LOAD? If you connect your DMM, set to read 'something' in ADC, directly to a battery, your DMM will be *BOTH* the LOAD and, for a short time, the MEASURING DEVICE. Then, either the fuse or the DMM will blow, and your experiment will be over.

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    Sigh Just the FAQs, Mam...

    Quote Originally Posted by fireguy View Post
    What about internal resistance? Can you use a DMM to measure the resistance within a cell?
    Sure!

    There are two methods listed in my Sig Line LINKs.

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    Rolleye11 Believe me I understand exactly what you are saying...

    Quote Originally Posted by Chase2b View Post
    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?
    What's M?
    Quote Originally Posted by Chase2b View Post
    ...
    Also trying to decide if I need a ZTS tester or just use a meter. (I know the ZTS put a load on it).
    Just use your new C9000. That's all you need...

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    Smile The Tale of George and John...

    Quote Originally Posted by bretti_kivi View Post
    I'd suspect it was millivolts...


    Quote Originally Posted by bretti_kivi View Post
    ...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...
    I understand what you're trying to explain, but, I believe that you have a few things reversed:

    ...Higher internal resistance - can't hold the charge and can only discharge slower...

    Due to the damage (higher internal resistance), John might still be able to supply 2700mAh total, but only at the rate of 100mA. Any faster / higher and his voltage drops (and he stops moving). John can still finish the race, but, it will take him a longer amount of time (Turtle).

    Without the 'speed governor', George can sprint to the finish line at 'full speed' (let's say 500mAh), arriving in much less time (Hare).

    If George and John are harnessed to the same wagon (in series), George will be limited by John's capacity. When John "drops dead", George is stuck...
    Last edited by TakeTheActive; 02-06-2009 at 12:37 PM. Reason: Fix typo - THANKS Cemoi!

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    Default Re: The Tale of George and John...

    Quote Originally Posted by TakeTheActive View Post
    Due to the damage (higher internal resistance), John might still be able to supply 2700mAh total, but only at the rate of 100mAh. Any faster / higher and his voltage drops (and he stops moving). John can still finish the race, but, it will take him a longer amount of time (Turtle).

    Without the 'speed governor', George can sprint to the finish line at 'full speed' (let's say 500mAh), arriving in much less time (Hare).
    In this case, the damaged cell with high internal resistance would work well in a low-current device such as a tv remote control? If we assume that the damaged cell could still retain as much capacity as a cell in good condition, and that there was no self-discharge, then both would work equally as well in this application. Of course, these two conditions never exist.

    John (but no relation to George's brother mentioned previously in this thread)


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    Lightbulb Re: Volts or mAh...which is more important?

    *FINALLY*, getting to the original question:
    Quote Originally Posted by Chase2b View Post
    ...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?
    Wrong! As narrated by bretti_kivi in the 'Tale of George and John', it's BOTH!

    But, not CHARGED Volts - UNDER LOAD Volts (which are affected by INTERNAL RESISTANCE).

    That's why you'll see folks posting different capacities for the same Make/Model cell (i.e. 2000mAh AA Eneloops) and questioning their cells, their new C9000, etc... If you want to compare, you have to follow the standards - discharge at the 'Standard Discharge Rate' of 0.2C. Discharge at 1.0C and the capacity reported will be lower; discharge at 0.05C and the capacity will be higher. When the voltage reaches 0.9VDC, the test ends - even if the 'Open Circuit Voltage' climbs back up. That's why you can perform a 0.5C discharge AFTER a 1.0C discharge and get more current out of a cell - less effort is required. It's like you doing 10 reps of 100 lbs and can't do #11. Rest a bit and then try 50lbs - maybe you can do 4 more. When you can no longer lift 50 lbs, rest a bit and try 25lbs - maybe you can do 2.

    SilverFox has explained this MANY times in the CPF Archives - several of his posts are referenced in my Sig Line LINKs.

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