How to Know a Fake 18650 Battery

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

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.

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27 Discussions

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aleggert52

4 months ago

A good article weight of 45g or more is the easiest clue to a fake 18650 battery! Generally speaking most batteries made in China that are labeled over 2600mAh are fakes as to there mAh rating. China's highest capacity for 18650 is 2600mAh as a rule of thumb. There are a lot of fake labeled and fake 18650 batteries being manufactured in China these days. Be sure what you are buying from China. It is worth it to get a confirmation from the manufacture as to the 18650 batteries weight and real capacity in mAh, not peak capacity!

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arvevans

2 years ago

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.

3 replies
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DanieleT15arvevans

Reply 10 months ago

3.2v? That is not correct at all. Just look at the datasheet of a LG Choco 18650 battery. It's cut-off voltage is 2.5v. Even most battery chargers like the IMAX B6 will discharge down to 3.0v when testing batteries.

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mc172arvevans

Reply 2 years ago

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

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texas hankmc172

Reply 2 years ago

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.

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Douglas75

3 years ago

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.

Douglas

4 replies
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Chris TibbMDouglas75

Reply 2 years ago

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.

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Eddieb1213Chris TibbM

Reply 2 years ago

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.

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danleowDouglas75

Reply 3 years ago

Thanks Douglas, your information helps.

Daniel

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Chui Lerhern

2 years ago

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?

1 reply
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danleowChui Lerhern

Reply 2 years ago

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

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M.J3

3 years ago

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

https://plus.google.com/u/0/photos/104329020925538604658/albums/6220722228646169665

Do not try at home without knowledge AND protections

2 replies
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danp70M.J3

Reply 2 years ago

Thanks for your knowledge

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wasteoinc

2 years ago

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..

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nunyafb

3 years ago on Introduction

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

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billbillt

3 years ago on Introduction

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...

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

1 reply

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.