Introduction: How to Know a Fake 18650 Battery

An average genuine 18650 batteries will weigh about 45g and no nothing less than 42g. You can see I have a fake 18650 battery in the pic weigh 32g only and the genuine 18650 battery weight 45g. Some genuine 18650 battery can weigh more than 50g. Good brands will tell you the weight of the battery.

You can use a digital kitchen scale.

Why fake 18650 battery weigh less?
That is because inside is a smaller battery with step up circuit which wrap in layers of paper and stuffed inside a 18650 battery size case then heat shrink in a tight plastic label sheet to make it look real.

Genuine sellers will specify battery weight in their product description/sheet.


arvevans (author)2015-12-21

High cost Li-ion cells contain a MOSFET in one end that shuts off once the battery gets down to 3.2 volts. This is the MOSFET turn-on voltage and is used to protect the cell from discharge below that voltage. If you discharge it below that voltage (difficult but it is possible) it is very difficult to restart the charge process because the charging current is not adequate to force battery voltage high enough to turn on the MOSFET.
Since the MOSFET "ON" resistance is only a fraction of an ohm it does not significantly reduce battery maximum current to have it in series with the cell.

Many so-called "fake" Li-ion cells do not include this protection device. This lets them actually have more chargeable material inside, and thus their higher than normal current and capacity. But this high capacity comes with a caveat...if you discharge them below 3.2 volts (remember, there is no low voltage protection) the cell may be damaged. Typically these damaged cells will not retain a charge for as long as a virgin cell might, or they might even overheat and catch fire when charging or discharging at high current rates.

On higher cost (i.e. non-fake) Li-ion cells you can usually feel an insulated metal strip down the outside of the cell covering. This is the sensor lead that provides gate voltage to the internal MOSFET switch. So-called ":fake" cells do not have this strip.

mc172 (author)arvevans2016-01-21

Can you show me a datasheet of an 18650 cell, or any Li-ion cell which describes this built-in MOSFET?

texas hank (author)mc1722016-10-26

If it's a single mosfet to disable discharge, its body diode would still allow charging of a deeply discharged cell. The safest way to attempt recovery of a deeply discharged cell is to attempt recharge at low current maybe 0.1C or 250mA max for an 18650 for up to 10 hours or so. If it's voltage recovers to normal minimum or more (but don't let it get over 4.2V) congratulations!!! If it doesn't, the cell is garbage now.

Douglas75 (author)2015-11-18

Yes, I to got caught purchasing FAKE UltraFire 18650 Batteries. I was able to go back to mu eBay purchase history and discover the FAKE 18650 battery sellers. THEY ARE: ebanlan, hksells, yallstock, led201314, laptopz-outlet, hkiron-aus. I reported this to eBay but received no responses. In total, I purchase 32 batteries which I must re-purchase. Need more info? Just ask.


Chris TibbM (author)Douglas752016-02-06

You must not know how many Battery manufacturers there are in the word for 18650's . There are ONLY 5. Aspire being the newest, with Sony, LG, Samsung and the Leader Panasonic the rest are simply rewraps of the subsequently lower grades on those 5 production lines Bins A-E A being the best and gets the company TM logo the rest as I mentioned are wrapped by those other companies that purchase from the B-D bins. So in other terms those FAKE Ultrafires are not even Ultrafires lol.

IceC3 (author)Chris TibbM2016-09-24

In the word? What "word"???

Eddieb1213 (author)Chris TibbM2016-08-26

I don't know how other people haven't realized that yet. Or you can go to moochs 18650 battery results. He test and shows data to all the real 18650 and how many companies ly about the amp and MHz on 80% of 18650s.

danleow (author)Douglas752015-11-18

Thanks Douglas, your information helps.


Chui Lerhern (author)2016-09-03

Thanks for your advice, i got that my 4 batteries bought are fake. But anyway, if the battery is fake,how much is its capacity?

danleow (author)Chui Lerhern2016-09-04

Is hard to tell, it can go as low as to 600mAh

18650 battery made it! (author)2016-03-25

A weight check is a great idea. I have attached a photo of the portable jewelry scale I use to quickly check cell weight.

But before you buy cells and check weight you should do a simple information check.

~~Is the cell advertising higher than 3600mAh?~~

~~If so, are you sure it is a lithium-ion 18650 cell?~~

If so, you have found yourself a fake.

(Note this was written on March 2016, however even be the end of 2017 we are not likely to readily exceed 4000mAh)


M.J3 (author)2015-11-24

From ebay. 4200mAh, but only 650mAh in use. I was wondering why:

Do not try at home without knowledge AND protections

danp70 (author)M.J32016-01-05

Thanks for your knowledge

critterfluffy (author)danp702016-03-11

Didn't see a reply so I decided to look. Found this one at Adafruit.

There is a MOSFET protection board listing in the datasheet on page 8 along with a circuit diagram. Hope that helps.

wasteoinc (author)2016-02-25

another problem that the weight test wont catch is the used 18650 battery. You buy them as new but they are actually old laptop bateries with reduced capacity from time not from design..

nunyafb (author)2015-07-20

Maybe this is stating the obvious but to everyone who is complaining
about this Instructable just add this simple little step. use this as
your first step to determine if your battery is fake. Really this is
helpful to say otherwise is foolish. Thank You

billbillt (author)2015-07-19

I got cheated a few years ago by these "fake" batteries on Ebay... I did not know at the time that people would go to such lengths to swindle a naive buyer like me... They were the "AA" size and were very cheap with free shipping... Needless to say they would provide current for about two minutes... The outer shell was very well made and looked like stainless steel.. I cut one open on my lathe and found what looked like a scrap of paper about the size of a folded up postage stamp inside...LOL!... Thanks for posting this warning and instructions...

martin.schmiedl.3 (author)2015-04-08

I'd love to see a capacity test of the 5000mAh battery which you identify as "not fake" :D

As far as I know, the best 18650 on the market right now has about 3400mAh

I put the 5000mAh into A5 powerbank and it fully charge my iPhone 3.5 times for the first 5 cycles and then the capacity kept dropping to 1 time. So the capacity was true only for the first 5 cycles.

domints (author)2014-08-31

So how are you going to prove your theory about these being fake? Just weight doesn't mean anything at all. They are just made in other technology - 18650 is just type of case, and inside can be completely different type of cell. Beside the difference between li-po and li-ion, which both could be stored in 18650, there are at least few types of both differing for example type of material on cathode, which could change the weight.

danleow (author)domints2014-09-01

Battery weight may vary among manufacturer but a little bit of common sense will tell you something is not right when the battery is about 8g lighter. Besides I have opened up a few of these fake batteries in the past, they are much smaller battery wrap in paper inside with step up circuit. I didn't make videos of it because other people have already made videos opening up these batteries... some videos below made by other people.

You are right, there are weight differences between Li-ion and Li-po. Li-ion compound which has density of 3.6g/cm3 and Li-po has density of 2.5g/cm3. So lets say a 18650 battery contain approximately 75% of this compound inside it and the other 25% for other materials. So a standard 18650 battery would have a volume of 17cm3 and 75% would be 12.75cm3. Li-ion compound alone would be about 45.9g then If it is Li-po would be about 31g. But my point here is that most of these battery claimed they are Li-ion batteries which is norm to all of us. Besides I find really hard to get Li-po 18650 batteries.

domints (author)danleow2014-09-01

But as you can see in first video, fake cell didn't differ by the weight, but the inner things, and the capacity. So as you can see, weight doesn't tell anything, and as you calculated, the ones you marked as fake, could just be li-po, not li-ion. To tell if it's fake just measure its capacity ;)

danleow (author)domints2014-09-01

Haha! the video shows that guy is pulling out a Li-po battery out from Li-ion case (Ultrafire label). Like I said 18650 are mostly Li-ion, no one would want to buy a 18650 Li-po battery. Li-ion has more energy density than Li-po.

domints (author)danleow2014-09-02

I think the li-po has higher energy density - More energy from lower size. And other advantage is that li-po's have higher discharge current and can survive more charge-discharge cycles. They aren't such bad, they're later technology.
And I see that the battery from which he took the smaller li-po weighted the same as real battery.

danleow (author)domints2014-09-02

Li-po has lower energy density (read this article: &

Besides Li-po battery has very specific applications such as for mobile phones (because it can be shape) and in flying remote controls (because of its weight). In addition, Li-po uses only specific Li-po charger (quite expensive) to charge its Li-po batteries. I have DJI phantom uses Li-po battery and is not easy to maintain needless to say for general use such as 18650 bat. Back to my point, everyone (or general population) assumed that 18650 battery are li-ion not li-po.

vikyleon64 (author)2014-09-01

ottima idea bravo

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Bio: Tech nerd like web technologies and gadgets. Kitesurf on weekends and recently got involved in 3D printing technology.
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