How To Identify Fake Lithium ion Battery

Dec 06, 2022 | XTAR

People often ask on social medias where they can buy authentic 18650 or 21700 lithium-ion batteries, and whether the batteries they buy are real or fake. Now that buying online is son convenient, there are many online channels selling 18650, 21700 and other lithium-ion batteries, such as AliExpress, ebay, and various websites, but the quality of these batteries is uneven. This article will tell you what a fake battery looks like and how to tell if the battery you buy is real or fake.

The performance of a battery mainly depends on the quality of its inside original cell. Top-brand original cell manufacturers include Panasonic, Sanyo, Sony, etc. Some not-so-famous Chinese battery manufacturers also make high-quality primary cell.

There are currently three kinds of “fake” batteries. 

Firstly, some batteries are not fake but “empty”. Using some relatively small primary cells inside the battery, coupled with a boost circuit, finally keeps the fullness of the package within the shape of the battery. In this case, the authenticity of the battery can be identified by weighing. For example, the weight of a protected 21700 battery 5000mAh is about 70g. If the actual weight of the battery you bought is only 40g, it is very likely that you bought a fake battery.

Note that even with real batteries, different capacities can make a difference in weight. The larger the capacity, the heavier the weight. For example, a 20700 3000mAh battery weighs only 60g, while a 21700 5000mAh battery weighs 70g. For batteries with a small difference in capacity, the difference in weight is almost negligible.

Secondly, new wrap wraps the old battery. Some unknown battery manufacturers replace the recycled old batteries with new battery wraps and package them as new batteries for sale. These old batteries have high internal resistance, low actual capacity and shorter cycle life.

Thirdly, exaggerate the nominal capacity. This kind of battery is not so much a fake battery, but just as an exaggeration. As in the second case, anyone can cut off the battery’s shrink wrap and replace it with a new wrapper with whatever markings they want on it. These repackaged batteries may simply be remarketed batteries, or actual counterfeits of popular brands.

In addition to capacity specifications, there are also safety features, and the presence or absence of battery protection circuits also come into play.

Then, how to identify a fake lithium ion battery? There are four tips.

First, pay attention to the nominal capacity. On the Lithium ion battery market, the maximum capacity of the 21700 battery is about 5000mAh, and the maximum capacity of the 18650 battery is about 3600mAh. If the nominal capacity of a battery is too much higher than the above value, it is necessary to consider carefully before you buy it.

Second, test the battery capacity. When evaluating a battery from a new supplier, you should perform a capacity test, discharge the battery to its rated cut-off voltage, then test charge cycles to see how much charge is needed, then discharge at slow and fast rates to see the results of these tests. Discharge rate matters! The slower the battery is discharged, the more total charge can be gained from it. Therefore, the same battery can have different capacities depending on its use.

For example, an INR21700 4000mAh unprotected battery is suitable for high drain devices such as electronic cigarettes. This battery can reach a continuous discharge current of 40A but has a short work time. And a protected 21700 5000mAh battery with discharge current of only 10A has a longer run time, which is very suitable for LED flashlights.

If you don’t have professional battery testing tools or don’t know much about electronic knowledge, you can buy smart battery chargers with testing functions, such as XTAR VC4SL, VC8 PLUS, VP4 PLUS. These three chargers can test the real capacity and the internal resistance of the battery. Just put the battery into the channel, switch to grading mode, the charger can automatically test the real capacity of the battery for you through chargingdischarging-charging cycle, no other actions are required.

Third, choose a reputable brand. A reliable lithium battery supplier has very strict quality inspection requirements and processes to ensure that wholesale lithium-ion batteries are in high quality. Therefore, when purchasing batteries, try to find a professional battery manufacturer, such as XTAR.

In addition, don’t only care for the cheap price. If you plan to spend 10-20 dollars to buy a powerful LED flashlight which also provide with a free battery and charger, dont expect the quality of the battery and charger to be good. A quality battery is definitely worth more dollars you pay for it.


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