I purchased a torch (flashlight) on eBay recently. It was described as using CREE T6 LED array, and supplied with two 4200mAh 18650 Li-ion rechargeable batteries with charger for A$25 inc post.
Above, the cells are clearly marked 3000mAh, way short of the advertised 4200mAh… but what is their actual capacity.
Above are the results of discharge tests, the first digit is the cell number and the second is the test. The first test is charged with the supplied charger, the second test is with my charger.
The supplied charger clearly does not charge the cells fully, and on test, it charges to 4.1V max, way short of the needed 4.3V so capacity is limited to 66% of that using a good charger..
Even with my charger, the capacity is only one third of the marked capacity, and one quarter of the advertised capacity.
This experience seems typical of Chinese sellers of 18650 batteries.
The seller did not concede that the charger is faulty, but promptly offered $10 refund for the cells, which was accepted.
I will use a Panasonic cell which my tests have shown to have capacity close to their ratings.
If you buy these things without testing them, you are probably being duped.