Sorting my batteries was made easier with a simple inexpensive battery capacity tester.
I found a wide variation in my own assortment of various 18650 Li-Ion cells. Now each cell has a number, the milliampere-hours (mAh) the battery achieved on the tester.
[click any pic to enlarge]
The one pictured had been running on the tester for over an hour. At the time of the picture, that 2600mAh battery had achieved 1716mAh (the display shows amp-hours ie 1.716 Ah). The final capacity is determined automatically by the tester when the battery voltage falls below 3 volts, the test is stopped and the final Ah shows flashing on the display. For this battery, the final was 2.758 Ah (2758 mAh).
This one battery is my BEST battery and the ONLY one that achieved a result on my tester greater than what was branded. None of the rest achieved branded capacity out of 15 cells tested. Bought from various sources, my 18650's cost me between C$7 to $15 each.
I am using the ZHIYU ZB2L3. Mine came from Banggood product ID: 1112859 in a little over a week after I ordered. The units I received were v2.3a.
ZB2L3 is a small circuit board which discharges a test battery into a resistor while measuring battery voltage and the current delivered to the resistor. ZB2L3 calculates the mAh. While testing, the display cycles three numbers and an LED at the side of the display shows alternately amp-hours, amps and volts. You can see a video here.
The micro USB cable only supplies 5 volts to the ZB2L3, not data. Since this is a complete discharge test, the ZB2L3 must have an alternate source of power hence the USB connection. Almost no energy is drawn from the USB. You can plug it into any USB charger or port. It will not charge the battery.
There is no data analysis available from the ZB2L3 other than from the display. I'd love to know that there was a way to capture a discharge curve such as this one, to explore different discharge rates and temperatures.
Two power resistors came with my ZB2L3. I used only one for all of this first round of tests. By using one of the supplied 7.5 ohm 5 watt resistors, the battery at 3.7 volts was seeing about a half amp of draw. This is (3.7X0.5=) 1.8 watts which makes the little square 5 watt resistor very hot, too hot to touch. That is why I have a cardboard sheet under the test, to protect the desktop. In hindsight it should have been a fire-proof insulating sheet. The battery gets slightly warm as it's working pretty hard.
I got the 18650 size battery holders from Banggood also. These I won't recommend. Although the battery should be held firmly against the contacts, with these battery holders it is difficult to remove the battery. The wires are very flimsy and probably contribute some voltage drop to the battery voltage measurement. Wires to the battery should as short as possible and a larger gauge wire. The contacts in this holder probably wouldn't handle soldering well. I will order better holders.
This test is a vivid demonstration of how much energy is stored in these little cells. The resistor is too hot to touch for several hours.
The ZB2L3 can be used for a range of batteries up to 12 volts and measures up to 9999 Ah. The value of the resistor can be adjusted to change the discharge rate up to 3 amps maximum but you must keep safety in mind of course.
Thanks for your interest,
George Plhak
Lions Head, Ontario, Canada
The battery flipped over to show the branded capacity tested at only 795 mAh, the lowest of this batch of "6800 mAh" batteries.
As is my custom, this is not a paid review nor do I receive or solicit any product in return for writing. I am not selling these products. Just ideas. I don't get a commission. I don't show ads. I don't have a fundraising or patreon page.
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