Introduction: Capacity Test of Fake 18650

Picture of Capacity Test of Fake 18650

In this Instructables let's find the capacity of Fake 10400mAh Power bank.

Previously I used This power bank to make my own power bank because I bought it for $2.

To watch Video for this Project -

And don't forget to subscribe to my channel

So let's get started

Step 1: Opening

Picture of Opening

Let's first open the power bank

One's we have opened it cut the wires of power.

since there are 4 batteries and the total capacity is 10400mAh so the capacity of each battery is 2600mAh

Step 2: Charging

Picture of Charging

Battery was not fully charged so first charge.

let's first charge them using TP4056 module

Step 3: How to Calculate Capacity

Picture of How to Calculate Capacity

We can simply use 1ohm 5 w resistor in series with the battery to test the capacity

but, voltage will decrease over the time and so our current ( resistance will be 1ohm)

and in this case we need to use integral function which is quite inaccurate

Step 4: LM358

Picture of LM358

Since using integral will be quite inaccurate let's use constant current source.

we can built a constant current source using LM358

let me explain how it works

1) When Vin is higher then Vref output is high which turns our MOSFET On

When MOSFET is trued on there is voltage drop across the resistor and our Vref is now High

2) When Vref is higher than Vin Output is Low and this cycle repeats

Step 5: Capacity Test !

Picture of Capacity Test !

One's the circuit is done adjust the potentiometer to get the current of 1A

It took 15 min for the battery to discharge completely.

Step 6: Calculation Time

Picture of Calculation Time

Alringht so the,

Current was 1A

and time was 0.25 hr

so the capacity of the battrey is.....










Step 7: My Thoughts !

Picture of My Thoughts !

I think they forgot to divide Every thingby 10

Because Actual capacity of the Power bank 1000mAh and not 10400mAh


The capacity of battrey is 250mAh and not 2600 mAh

Hopefully you like this project dont forget to like and share

And yes do check out my channel on Youtube - Click Here

(If there is Any Mistake Please feel free to tell me in comments)


Nice Physics Math calculation in Electronic Field my friend... Continue studying this field and learn more about Quantum Electron Arithmetic Calculations and Quantitative Arithmetic Calculations of Electrical Energy... Excellent demonstration my friend...

martinhui (author)2017-06-10

I used a discharger not known the discharge resistance, the values shown to discharge 1A current from 4.20V to 3.0V took 23 min 17 sec, can you calculate the mAH?

Nematic! (author)martinhui2017-06-10

2600 mAh

martonthenagy (author)2016-09-01

Here you can find a very good list of 18650 battery tests, including top brands, and cheap/fake ones too.

250mAh seems unlikely low. I would repeat it, even with lower currents.

rkrishnan7 (author)2016-08-14

The quoted mAh capacity on most battery labels are for smaller current draws; thus, a 1000 mAH battery seldom delivers 1000mA for 1 hour. However, it will come close to delivering 10 mA for 100 hours! Of course some lousy batteries won't even do that ! Your test should be really conducted on the expensive (not cheap imports) to make sure. Somehow I suspect even they will not be significantly better, at least for the extra bucks you'd have to pay for them.

pkmonster (author)2016-08-09

I think we probably must be careful with products made from China.

redsunmtm (author)pkmonster2016-08-09

do you know one constructor of batteries that is not made in china ?

for my part... no one !

efoster6 (author)redsunmtm2016-08-10

samsung, LG, Panasonic,motoma are 4 different brands that I recommend having tested both for capacity and load capability

JohnnyMorales (author)efoster62016-08-13

And they are often the most counterfeited brands too boot.

It takes a bit more effort to beat the counterfeiters at their own game than simply buying brand label.

About the only certainty is brand name batteries are always by far the most expensive costing 2-4x as much as the generics and the counterfeits.

Even then you could still buy a bad one simply going on price alone from a seller who takes advantage of people who think price = quality.

pkmonster (author)redsunmtm2016-08-10

I think probably many parts or components of electric device are made from China. But I highly recommend that we should not buy products with unfamiliar brands, low price, no warranty that comes from China.

I agree that Xiaomi is a good and big company which supplies many useful products. However, there are numerous companies that they are making largely range of fake products. We should be aware of that.

On the other hand, we can use various electric devices with global brand such as LG, Samsung, Electrolux, Sanyo, Sony.. These are made from Korea or Japan or even Hong Kong.

Nematic! (author)redsunmtm2016-08-10

Panosonic are made in Japan I guess

Mike-Gyver (author)pkmonster2016-08-09

Very true we must be careful of things made in China, but good luck finding things that aren't made there these days! I think the best thing is to pick major brands, read reviews, etc.

GavinF2 (author)Mike-Gyver2016-08-09

You should be wary of buying by price rather than quality.
If you want to buy from a foreign supplier in any country and pay the lowest possible price you will not receive a good quality product and will have no warranty
If you buy from a local retailer you will be able to return it so they make an effort to make sure they have sourced good quality parts and will charge you accordingly.

JohnnyMorales (author)2016-08-13

As Li-Ion batteries age, they lose capacity.

Also an inadequate charger can cause a rapid reduction in charging due to a poor match in the specific requirements for each brand of li-ion battery out there.

If you're going to try and figure out the capacity of used batteries like that try an opus charger custom made to charge li-ion batteries and rated highly. There are several versions out there, and I think the one that gets it right the first time are chargers with hardware update 2.1 and newer.

While they can also be counterfeited, the manufactured does try to make it possible for consumers to have confidence in their purchase. You do have to read the small print in ads though, and see if it comes with some sort of hard to imitate proof of origin.

Opus chargers give a good statistical breakdown of what to expect from both a new battery and old ones after it charges.

It also has a discharge/refresh cycle for old batteries that can help restore some capacity lost due to time or being charged by a poorly designed charger.

It has several other functions for li-ion that heavy users will find very useful.

To be clear, it's not just the li-ion batteries mass produced in China by anonymous manufacturers that are sketchy, but also the cheap, poorly made mass produced li-ion chargers that are a big source of the problem often attributed to the batteries alone.

Using a poorly made charger can dramatically shorten the life of even the best made li-ion battery.

I should have said specifically made to charge li-ion batteries that can also charge other types of rechargeables, because it seperate circuitry for each to match their specific requirments, rather than custom mad.

milessw (author)2016-08-11

Your not the only person to notice this practice by Chinese suppliers of Li-Ion products.

Battery capacities are often misrepresented and they seem to get away with it.

artmez (author)2016-08-10

Your analysis of the op amp based constant current source is incorrect. The FET is not SWITCHED on and off. If it were, this circuit would be an oscillator (which is possible with an unstable circuit). What a constant current should do is BIAS the FET so that the FET is only biased "on" enough to ensure that the Voltage drop across the current sense resistor is sufficient to balance the op amp's reference Voltage input. This is done within constraints of the op amp's open loop bandwidth.

Not all Chinese parts are bad. They can't be, since even Japan outsources manufacturing to China. I suggest you repeat your testing on "known good" batteries and compare the results before you make your final judgement.

pkmonster (author)2016-08-10

I think that we can have another solution for this by buying good cells and replacing into the case :))

pkmonster (author)2016-08-10

I think that we can have another solution for this by buying good cells and replacing into the case :))

Elec_BM (author)2016-08-09

I've used profession load banks (cost $1000+) to measure battery capacity of the Chinese ebay purchases and got the same result. They outright lie about the capacity, and don't seem to care about the repercussions (lets face it, what can you do?). The only solution I've found is to pay retail prices at a local store where you can take it back if its not up to scratch.

Nematic! (author)Elec_BM2016-08-10

I think there was no need to spent $1000 for testing the capacity :P

Elec_BM (author)Nematic!2016-08-10

Well yes, I'd spend that money buying better batteries instead of testing dodgy ones too. But if you work in electrical engineering, and already have access to that equipment.....
Anyway, just letting you know it wasn't test method or circuit calculations that was giving you that result - it really is the batteries at fault.

RockeyD (author)2016-08-10

what is a power bank? is that british for battery pack or somthing?

wlim (author)2016-08-09

what was the criteria for fully discharged? The protection circuits do not kick in

until around the 2.8v range for a Li-ion battery. Also the charger (I think) is one that cuts off at around 4v which according to Battery University may only give a 85% charge. So without knowing these things, we might say that it may be less but not by how much. A real low guess of mAh might be the time to go to 2.8v times 2.8A (2.8v=1ohm*2.8A)

Nematic! (author)wlim2016-08-10

These are not having integrated protection circuit

wlim (author)Nematic!2016-08-10

yes but i was using it as a possible criteria for fully discharged. Or rather what a manufacturer might use to calculate capacity

meanblackbike (author)2016-08-10

Great instructable.

I made something more complex - using arduino to test and calc and show the real capacity on a screen.

Probably I have to make an instructable for that.

Basically I used 1 ohm and heated it but I used MOSFET that has neglegent resistance of 0.01 (those high current IRF44) so when the 3V are reached I stopped discharging.

The Arduino calcs all the resistance and voltage and - only NCRs purchased from banggood was good at 3.1Ah also I tested the pink ones from the same site (should be Samsung unbranded) and Sanyo unbranded all was as advertised - but others noname (no brands not unbranded) those are useless non of them have even 2000mAh or 2Ah so by those I tested and won't sorry - NCR that I tested was dark blue/cyan colored - there are new that claim 3.4Ah but not purchased or tested.

If interested I will publish my battery capacity tester :)


sue.donim.144 (author)2016-08-09

you said you used this battery before hand. did you use this battery before or is it new ? how much use ? batteries deteriate over use and time . age plays a factor too . were the batteries date stamped for expiration ? i have found that even american batteries may not be mah stamped.

Nematic! (author)sue.donim.1442016-08-10

I purchased new one for the video as it cost only $2

sue.donim.144 (author)Nematic!2016-08-10

o.k. wow then it was misleading. thanks for the info on how to do it. wish most rechargeables lasted longer. some solar lights are now using batteries shorter than AAA (aaaa?) and 100mah. hard to recharge in a charger.

e5frog (author)2016-08-09

Comments to the other commenters: Sounds like people that have commented thinks "China" is a single company or person... There are of course good and honest companies in China as well as a bunch of cheap crap. Don't buy the cheap crap - you know it's crap and you shouldn't expect anything else.
It doesn't say .250mAh as in 0.250mAh, it just happens to be a dot there like all the dots before presenting the result. It clearly says 250mAh in the image. I'm sure he meant battery as well and not "battrey".
Even if some people have comments on the measuring method, it seems the capacity is a lot lower than it's supposed to be, right?

Nematic! (author)e5frog2016-08-10

Ya there was typing mistake about .250 mAh

e5frog (author)Nematic!2016-08-10

It would be clear to anyone he meant...
. wait for it
.and not 0.250mAh

Dots were added as decoration - in anticipation of the result, not as a decimal comma.

miragempro (author)2016-08-10

Sorry, google translator does not translate correctly. the battery cable, where you bought? battery door that appears in the tutorial? where you bought?

efoster6 (author)2016-08-09

I had the same problem so I bought a nokoser digital charger to test them and I did not find any batteries that had the rated capacity so I now only buy samsung panasonic or if you know a reputable battery agent try them. I have done a bit of research and it is not unknown for them to put a very tiny cheap battery so you will get a voltage reading when tested and then fill the cell up with some unknown white powder.

Nematic! (author)efoster62016-08-10

Well said I did same test with Some orignals I got The expected result

miragempro (author)2016-08-09

Hello, thanks for the tutorial.

This battery door plastic and the two wires, which bought? in Brazil has for this battery 6800mA

Nematic! (author)miragempro2016-08-10

WOW :P I have see the capacity rated with 9000mAh

wcgems (author)2016-08-09

I've noticed this a lot in Chinese electronics (and others things) that they tend to be off by a factor of 10.

Nematic! (author)wcgems2016-08-10

Hahaha Its true

Mihemine (author)wcgems2016-08-09

It's on purpose :p

KabelV (author)2016-08-09

you are forgetting one crucial point....The DC-DC converter !.

You need a bit more than 5 Volts to charge someting. The battery itself gives only 3,6V. Then the capacity will decrease a lot more

Nematic! (author)KabelV2016-08-10


jim.buchanan.165 (author)2016-08-09

I wrote an article about testing the capacity of AA primary cells, I've documented it here:

It uses an Arduino to measure the discharge characteristics of the cells. A similar method could be used on 18650 cells, for those who are interested in watt hours, a small change to the post-processing software could be made. I used a Linux machine to run the post-processing software on, with thw Windows 10 Anniversary Edition, you can install the Linux environemtn and perl, and run it under Windows.

Nice Articale but I personally like to keep thinks simple

ac-dc (author)2016-08-09

Your testing is not really relevant unless you only cared about effective capacity powering something in particular that needed 1A current.

It is true that generic battery manufacturers wildly overrate their cells, but any battery manufacturer rates their cells at a specific current that is likely to be lower than 1A for generic cells. At lower current they have more effective capacity.

Now, if there were not a power bank but instead an industrial or true professional grade product, there might be a different standard, or actually two possible different standards.

1) The battery capacity at the expected power output (at 5V in this case), and perhaps the battery capacity at the max rated power output (at 5V).

2) No battery capacity rating at all! On an integrated product with batteries built in, in industrial settings especially, the current rating would be the output current rating at 5V, not peak, but mAh or Wh.

#2 above is really what would work best for consumers since it is most relevant to % charge of a device and in best cases how many charges it can provide for a device (> 100%).

Now to instead consider this specific power bank, the most appropriate current for battery rating would seem to be one where the 5V USB output was somewhere between 1A and 2A, depending on it's max output rating.

In that case, let's say 1A at 5V output, each cell would be draining at roughly 1/4th that since there are 4 cells, minus the efficiency loss of the 5V boost circuit which I will rate around 10%, so roughly each cell might drain at about 1A / [ 4 * 0.9 ] = 278mA

Nematic! (author)ac-dc2016-08-10

These battries cannot be charged upto 5 V max is 4.2 V

Battrey type - 18650

WayneT22 (author)2016-08-09

Your math is wrong. With a load of 1A draining the battery in a quarter hour the capacity is displayed either as 0.250 Ah or 250 mAh. If it was .250 mAh it would have discharged in one tenth of that time.

kevin.d.timm (author)WayneT222016-08-09

Though he wrote .250mAh his final computations show 250mAh (or .250Ah) - and he mentions too that the mfr must have missed the divide by 10 step

WayneT22 (author)kevin.d.timm2016-08-09

No, I see my confusion... the OP used a series of periods separated by two line feeds for dramatic effect. He put the 250mAh immediately after one of those periods.

About This Instructable




Bio: Hi, I'm Nemeen !, Electronic and robotics enthusiastic. This is my channel 'Nematic !' I will be uploading on and about awesome Electronics Tutorials, Projects and ... More »
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