# how to test a 4x 18650 battery pack?



## Gabe3 (Mar 13, 2009)

I want to test the 4x 18650 pack that came with a cree 3x light. can I do this without taking the pack apart?

heres the meter I'm using. I'm not sure if its on the correct settings. when I touch the battery's plug with the pos/neg it makes a little spark


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## Cat-man-do (May 16, 2004)

The setting on the meter looks correct. Here's the problem, no ones hands are steady enough to try to hold two probes to a plug end without shorting the circuit. That's probably the spark that you were getting. Most batteries contain a protection circuit that will cut off the current if current is shorted. When that happens the battery will now read zero.

What you need to do: Reset the battery by plugging it into the charger. The best way to measure the voltage on your battery is by buying a cheap MS type wire extension, cutting off one of the plugs and then baring the wires so you can easily attach the probes to the leads without shorting the circuit.


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## Gabe3 (Mar 13, 2009)

Cat-man-do said:


> The setting on the meter looks correct. Here's the problem, no ones hands are steady enough to try to hold two probes to a plug end without shorting the circuit. That's probably the spark that you were getting. Most batteries contain a protection circuit that will cut off the current if current is shorted. When that happens the battery will now read zero.
> 
> What you need to do: Reset the battery by plugging it into the charger. The best way to measure the voltage on your battery is by buying a cheap MS type wire extension, cutting off one of the plugs and then baring the wires so you can easily attach the probes to the leads without shorting the circuit.


thanks. I tried again with the multimeter on the same settings in the picture. I put the battery plug in a vice grip and held one probe on the circle metal piece and the other on the center piece. it didn't seem to matter if I swapped the black/red probes. I get a reading of 7.71v. is that voltage good? bad? I still have not plugged it into the charger yet.

do you know how I can check the mah? I tried all 4 settings in yellow next to the A on the multimeter but not getting any reading.


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## Gabe3 (Mar 13, 2009)

I plugged the charger in that came with the battery/light. it smoked and made a pop sound a few seconds later. glad i didn't plug the battery in.

I'm thinking I should get one of these magicshine chargers. this should be safer than the one I got right? (if I got one that didn't smoke, lol)

Action-LED-Lights ? Magicshine 1.8A Charger - MJ-6012

can this charge a 6 cell pack as well?


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## Kir (May 30, 2013)

MJ charger will work fine.
About battery pack - you want to test what? 7.71v is good, but that doesn't say anything about the quality of battery pack.


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## kgatwork (Oct 7, 2008)

Gabe3 said:


> thanks. I tried again with the multimeter on the same settings in the picture. I put the battery plug in a vice grip and held one probe on the circle metal piece and the other on the center piece. it didn't seem to matter if I swapped the black/red probes. I get a reading of 7.71v. is that voltage good? bad? I still have not plugged it into the charger yet.
> 
> do you know how I can check the mah? I tried all 4 settings in yellow next to the A on the multimeter but not getting any reading.


You cannot use the amp meter by connecting the leads like the volt meter. You are shorting the battery again when connect the amp meter setting to the + and - side of the battery. I hope that's not what you did with the power supply too, that would not be good. The amp meter measurements must be done in series, ie one end of the amp meter connects to the + on the battery, the other end connects to the + on the light. The - is not connected to the meter at all and must be connect between the battery and light.

To measure MAH ie capacity, you need to load the battery with a known load and measure time till the battery is fully discharged. So if you have a 1000 milli-amp load for 4 hours you get 4000 Mah.

You will also have to move the voltmeter + plug to the 20A plug when measuring the current load for the light. The light probably uses 2-3 amps on high and the multimeter as plugged in will only do 200mill-amp max.

This is basic electronics, if you don't really know what your doing you should do a little research before testing with your meter and batteries.


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## Gabe3 (Mar 13, 2009)

kgatwork said:


> You cannot use the amp meter by connecting the leads like the volt meter. You are shorting the battery again when connect the amp meter setting to the + and - side of the battery. I hope that's not what you did with the power supply too, that would not be good. The amp meter measurements must be done in series, ie one end of the amp meter connects to the + on the battery, the other end connects to the + on the light. The - is not connected to the meter at all and must be connect between the battery and light.
> 
> To measure MAH ie capacity, you need to load the battery with a known load and measure time till the battery is fully discharged. So if you have a 1000 milli-amp load for 4 hours you get 4000 Mah.
> 
> ...


ok thanks. guess I can't measure the mah then. I just wanted to see the mah since the battery is suppose to be 6400mah, its a cheap battery but wanted to know how close it is to 6400mah. once I get a new charger and get the battery charged I'll see how long it lasts on high with a fan blowing on it.

I never did anything with the charger, just plugged it into the wall and it smoked, then popped and smoked more. I did hear something moving around in the charger. very small like a piece of sand or dirt so I was kinda expecting something to happen when I plugged it in.


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## Kir (May 30, 2013)

It won't be 6400mAh, not even close. Expect 2000-4000mAh, maybe 4400mAh if you're very lucky.


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## kgatwork (Oct 7, 2008)

FYI:
If you really want to know the capacity of the pack, you could pick up a balance hobby charger with the ability to measure the capacity of your battery.
Goog luck.


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## Cat-man-do (May 16, 2004)

Gabe3 said:


> ok thanks. guess I can't measure the mah then. I just wanted to see the mah since the battery is suppose to be 6400mah, its a cheap battery but wanted to know how close it is to 6400mah. once I get a new charger and get the battery charged I'll see how long it lasts on high with a fan blowing on it.
> 
> I never did anything with the charger, just plugged it into the wall and it smoked, then popped and smoked more. I did hear something moving around in the charger. very small like a piece of sand or dirt so I was kinda expecting something to happen when I plugged it in.


If your charger smoked-crackled, whatever...don't use it anymore. Buy a new charger, they are not that expensive. I doubt your battery is 6400mAh but depends on what you have...4 cell, 6 cell? Anyway, when your battery is fully charged it should measure 8.4 volt when fully charged. If it's a little less don't worry.

Testing the the mAh rating of a battery is not always easy. Best way to do this is with a controlled current source ( compatible with your battery voltage ) with a suitable load. ideally something drawing around 1A. Some of the more expensive hobby battery chargers have a set-up that will discharge your battery and give you an Amp hour read out. Not sure they're really worth the money though unless you are a total battery geek.

Even if you know the true mAh rating of your battery you still need to know how long that battery is going to run your light system. While the mAh information is useful unless you know how that information relates to your lamp it's just a number. The most useful information you can have on your battery is , "How long will it power my lamp before it cuts out"? As much as a PITA it is the best way to answer that question is to hook it up to your lamp ( with a fan blowing on it to keep it cool ) and let it run on high till the lamp shuts off. Doing this though with some lamps could be problematic because some lamps if they over heat will power down automatically. Auto power-downs tend to skew any kind of run-time test.


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## JohnJ80 (Oct 10, 2008)

You could never figure out the mAH rating of the battery by just putting a load on it and measuring the voltage across it because the current and the voltage of the battery will change with time. You essentially would have to add up every instantaneous current over time to understand the capacity of the battery (i.e. the area under the curve of current produced over time).

There are chargers that exist that will do this for you. They fully discharge the battery from full charge and integrate the current over time as they discharge using a FET that operates to pull a constant current out of the battery (think of it as a variable load that is controlled by the charger). They then can also keep track of the current put back into the battery over time to get to the full capacity. Most of these chargers are for standard form factor batteries (ie. AA, AAA, 18650 etc..) but there are probably ones that do this for larger batteries with leads or you could adapt another standard factor charger but it's not going to be simple.

Using the ammeter above connected to the battery will pretty much blow the fuse in the ammeter because it will be a dead short across the battery. The "pop" you heard was probably something blowing up inside the meter, charger or battery pack when you did this before.

J.


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## -Archie- (Aug 25, 2013)

*Gabe3*, you can just measure real run-time of your light with that battery (use household fan to prevent overheating): knowing how long it works is even better than mAh value.

As for charger - yes, MS ones are good enough, so just replace your faulty one.


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## kgatwork (Oct 7, 2008)

JohnJ80 said:


> You could never figure out the mAH rating of the battery by just putting a load on it and measuring the voltage across it because the current and the voltage of the battery will change with time. You essentially would have to add up every instantaneous current over time to understand the capacity of the battery (i.e. the area under the curve of current produced over time).
> 
> There are chargers that exist that will do this for you. They fully discharge the battery from full charge and integrate the current over time as they discharge using a FET that operates to pull a constant current out of the battery (think of it as a variable load that is controlled by the charger). They then can also keep track of the current put back into the battery over time to get to the full capacity. Most of these chargers are for standard form factor batteries (ie. AA, AAA, 18650 etc..) but there are probably ones that do this for larger batteries with leads or you could adapt another standard factor charger but it's not going to be simple.
> 
> ...


You are absolutely right. I just put it in layman's terms as the OP doesn't know what he was doing with that meter.


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## Gabe3 (Mar 13, 2009)

thanks for the help. the pop wasn't related to the battery. the pop/smoke happened to the charger when I plugged it into the wall, battery was never connected. sparking was when I was testing the battery with meter incorrectly. that happened quite a bit till I figured it out, hopefully no damage was done to meter or battery. I did quite a bit of searching before I attempted to test it but nothing out there for testing a battery pack, or I'm using the wrong search terms.


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## Cat-man-do (May 16, 2004)

Gabe3 said:


> thanks for the help. the pop wasn't related to the battery. the pop/smoke happened to the charger when I plugged it into the wall, battery was never connected. sparking was when I was testing the battery with meter incorrectly. that happened quite a bit till I figured it out, hopefully no damage was done to meter or battery. *I did quite a bit of searching before I attempted to test it but nothing out there for testing a battery pack, or I'm using the wrong search terms*.


The hobby chargers I mentioned before will do what you want. They are meant for people who are charging batteries of different chemistries and different voltages. These chargers need to be set specifically for battery type, voltage and charge current level. This is why I never recommend them to people. The IMAX B6 is an example of a charger/discharger compatible with Li-ion batteries using up to 6 cells. If you really think you might want to buy one I would recommend e-mailing the people who sell them and asking what product would best serve your needs. _Since you want a discharger that will tell you the capacity of the battery you need to ask the seller if the one you buy will do that._

If you buy one of these chargers you will still need a way to attach the battery to the charger. If you buy the plug/extension and do like I suggested, all you have to do is attach the correct clip to the right wire and you're set.


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