I decided to test some Li-Ion cells in 18650 size available on the market (especially on Ebay)
and to find out the truth about their parameters, especially the capacity :).
For testing, I used my battery analyzer.
It turns out that buying the cheapest battery with the highest capacity isn't worth it.
The declared capacity of the battery often does not correspond to reality. The actual capacity can be up to 25x less!
Sometimes it is even technically impossible to fit the declared capacity into the size of a 18650 Li-Ion battery.
We often see Li-Ion cells with the capacity like 5800 mAh, 9900 mAh or even 12 000 mAh. In fact, 18 650 size Li-Ion batteries can't have
higher capacity than 3500mAh. It's just not technically possible. Usually the real 18650 cells tend to have a capacity of about 1800 - 2500 mAh.
There are also 3400 mAh cells, but the higher capacity is at the expense of lower allowed discharge currents.
Therefore, even in the modern cordless drills and other tools
we still see cells with only 2000 mAh capacity. If you see a 18650 Li-Ion cell over 3500 mAh, the capacity is fake.
The maximum capacity may improve with progress, but very slowly.
Also the weight of the battery can tell a lot. Real 18650 Li-Ion cells weigh about 40 - 48 grams. If the weight is lower, something is simply missing inside.
Most fakes I came accross weigh only about 25 grams. It is almost 2x less. You can tell it even just by holding it in your hand.
Fake cells are made in low quality and a considerable part of the space inside is empty. Capacity is very low, they don't last long.
Internal resistance is high, they can't supply much current. Additionally, due to poor quality materials, it may have a high self-discharge.
Fake batteries often say they have a built-in protection circuit, although they don't have any. Text on a fake cell often contains typos.
As I test more batteries, I add them to the table below. It appears that the typical capacity of a fake Ebay Li-Ion 18650 cell is only about 400-550 mAh
which makes them almost useless. Fake batteries try to attract the buyers by unreal, sky high capacity, fictive protective circuit and interesting printing.
Real batteries can also be bought for a good price. However, they are mostly hidden behind very simple printing and a low capacity.
The capacity just seems low in a comparison with fake batteries.
The higher is the declared capacity, the lower usually is the real one :).
In addition to fakes, we can also inadvertently buy recycled cells. These are old used and worn cells that have been given a new heatshrink foil.
They mostly come from trashed laptop batteries. The traces of the previous spot welds on the contacts are covered by new contacts.
In Asian countries, where labour is very cheap, this is a big business. Recycled cells can sometimes be still good,
but sometimes most of their capacity is long gone.
You can also run into rejected (defective) cells disposed of at the factory.
Recycled and defective cells are unfortunately not recognizable by weight, but you can tell them by looking at the negative terminal.
Remove a small piece of the plastic foil. If it's a recycled cell, you will see a piece of added circular metal sheet.
I measure the capacity at 500mA discharge current down to 3V. Before the test, I charge them at 500mA to 4.2V. The results:
| Photo | Maker | Marking | Declared capacity | Measured capacity | Protective circuit | Weight | Price |
|---|---|---|---|---|---|---|---|
. . |
- | ICR 18650 3.7V | 1 800 mAh | 1 843 mAh | NO | 43g | $ 1.88 |
. . |
- | ICR 18650 3.7V | 2 000 mAh | 1 984 mAh | NO | 44g | $ 1.88 |
. . |
- | No marking. Ebay listing says KR 18650 | 2 000 mAh | 2 391 mAh | NO | 46g | $ 1.50 |
. . |
- | SW18650 25HP 16F01 281856 | 2 600 mAh | 2 359mAh | NO | 47g | $ 3.20 |
. . |
DoublePow | ICR 18650 3.7V | 2 000 mAh | 1 986 mAh | NO | 44g | $ 2.50 |
. . |
DoublePow | ICR 18650 3.7V | 1 200 mAh | 1 111 mAh | NO | 37g | $ 1.65 |
. . |
TrustFire | IMR 18650 40A 3.7V | 2 500 mAh 9.25 Wh | 2 373 mAh 8.682 Wh | NO | 46g | $ 6 |
| Photo | Maker | Marking | Declared capacity | Measured capacity | Protective circuit | Weight | Price |
|---|---|---|---|---|---|---|---|
. . |
- | TR 18650 3.7V | 5800 mAh | 552 mAh | NO (says YES) | 24g | $ 1.50 |
. . |
GIF | NCR18650B 3.7V | 3000 mAh | 554 mAh | NO (says YES) | 24g | $ 2 |
. . |
- | IMR 18650 3.7V LI-MN 35A | 2 500 mAh | 496 mAh | NO | 25g | $ 3.30 |
. . |
GIF | ICR 18650 3.7V | 12 000 mAh | 538 mAh | NO | 25g | $ 3 |
. . |
GIF | TR 18650 3.7V | 9 900 mAh | 542 mAh | NO (says YES) | 24g | $ 2 |
. . |
- | TR18650 3.7V | 4 500 mAh | 453 mAh | NO (says YES) | 25g | $ 2.70 |
. . |
- | BRC 18650 3.7V | 5 000 mAh | 426 mAh | NO (says YES) | 24g | $ 2 |
. . |
- | LIR 18650 3.7V | 2 200 mAh | 934 mAh | NO | 37g | $ 2.20 |
. . |
UltraFire | LC 18650 3.7V | 3 800 mAh | 473 mAh | NO (says YES) | 31g | $ 3.20 |
. . |
UltraFire This is an old recycled (re-wrapped) cell from e-waste! | LC 18650 3.7V | 2 400 mAh | 1523 mAh | NO | 42g | $ 2.90 |
. . |
Gtlenergy LED Flashlight Expert | TR 18650 3.7V | 2 300 mAh | 949 mAh | NO (says YES) | 38g | $ 2.30 |
. . |
CASTNOO | 18650 LI-ION 3.7V | 3 000 mAh | 921 mAh | NO (says YES) | 36g | $ 2.70 |
. . |
SecurityIng | 18650 3.7V | 1 800 mAh | 854 mAh | NO (says YES) | 37g | $2.40 |
. . |
Feng Xing Hu Wai (fxhw.cn) Used, worn battery -spot weld marks covered! | 18650 Li-Ion 3.7V - 4.2V | 2 400 mAh | 803 mAh | NO | 43g | $1.55 |
. . |
Feng Xing Hu Wai (fxhw.cn) | 18650 Li-Ion 3.7V - 4.2V | 1 800 mAh | 1 104 mAh | NO | 36g | $1.30 |
. . |
"Samsung" | INR18650-25R SAMSUNG SDI 5 2G21 | 2 500 mAh | 1 791 mAh | NO | 43g | $3.50 |
. . |
"LG" | LGDBHG21865 Q313K082AG | 3 000 mAh | 1 703 mAh | NO | 44g | $3.50 |
. . |
- | NCR18650B Li-Ion MH12210 Made in Japan Ebay listing says button top but it's a flat top | 3 400 mAh | 1 796 mAh | NO | 43g | $3.90 |