Chinese gadgets could really save your day with their low prices but you should be extremely careful and suspicious about the quality of cheap products, especially when quality affects your safety. I bought a couple of 18650 batteries from ebay, keeping in mind they might be fake, but I was hoping I will stand lucky.
The listing was about “2x UltraFire 3.7V 4500mAh 18650 Protected Li-ion Rechargeable Battery”. I was sure they were not genuine Ultrafire and definitely not 4500mAh. The first impression when I hold them in my hand verified my doubts. They were really light with bad quality printed cover but I noticed a small distortion at the bottom. There was a circular PCB that was probably the protection circuit. This protection circuit is very crucial since these lithium batteries could explode if you overcharge or overdischarge them. Most genuine 18650 batteries’ weight is about 40-45 gr. Fake weigh a lot less.
I put one of them in a battery holder connected with a TP4056 charger module. Also I cut the trace of the PCB that was connecting a barrel jack to the battery’s negative pole. I connected the battery’s negative pole on B- and the barrel jack’s negative pole to OUT-. That way I am able to use the same battery holder to power my projects using its barrel jack. The input voltage of this module is 5V so it could be powered from a USB port. The output voltage is 4.2V. There are a few versions of these modules available. I used the newest version with a microusb connector and two extra components on board, a battery protection IC and a dual N-channel mosfet.
The charge current is programmed with a resistor(Rprog). It came with a 1.2K Rprog, setting the charge current at 1000mA. The charge current on these lithium batteries should be half the capacity they have or less(For a 2500mAh battery, charging current of 1A should be fine). A red led lights up while charging and a blue led when the current drops to 1/10 of the programmed charge current and the charging process is considered completed.
When I connected my battery the blue led was steady on and the red led was flashing indicating there was no battery connected. I was sure my batteries were not 4500mAh as they advertised and I couldn’ t charge them with 1000mA. I replaced the Rprog with a 4.7K resistor setting the current to 250mA. I connected the first battery again but nothing changed. I connected the second battery and the red light turned on.
While charging the second battery I removed the cover of the first one since I couldn’ t charge it and I thought it may be damaged. There was indeed a PCB at the bottom but someone “forgot” to solder the components on it. Apparently the PCB was not making contact with the negative pole of the battery preventing it from being charged or discharged.
I found that their capacity is less than 330mAh. The seller agreed to refund me but I’m really sceptical on buying no name batteries from China again. We should also consider how many dangerous unprotected batteries have been sold.
I got these batteries to use them with a Cree flashlight. I will continue to use them for experimental purposes but I will always charge them with a protection circuit and stop using them when the flashlight starts flickering.
There is a nice video of Julian Ilett explaining a lot about TP4056 lithium cell charger.