How to test 18650 batteries

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[ericklein]

There was a fair bit of voltage drop on the 2600mAh cell which leads me to believe it’s IR was quite high. Even the lesser quality batteries dropped to only 3.91V so I would definitely check the IR of those cells. A battery can still retain most of its capacity but have an extremely high IR. Or it could just be a cell with a low discharge rating. It’s hard to say as your battery capacity tester has a lot of resistance in the circuit between the small wires and the cell holders with springs.

The best cell holders are those using the Keystone design with leaf spring tabs. I’ve found the gold plated leaf springs to have the lowest IR out of all of them. The cheaper cell holders that have leaf springs use steel and add about 40mR of AC IR to your cell being tested. The gold plated Keystone add about 10mR AC IR when you measure a known cell by placing the probes of an RC3563/YR1035+ on the ends of the leaf springs where you would normally solder your wires. Using 29mR cells on a new cell holder I was getting results of 36-38mR so if you use some 16AWG or 14AWG wire for the connections to the power resistor and the board you should only add a couple more milliohms to the entire equation. That’s small enough to give you fairly accurate voltage drop measurement testing since it looks like you are using 8R resistors that give you exactly 0.5A on a 4.00V cell or 0.510mA on a full cell. That’s the downside to power resistors, without a constant current source measuring voltage drop becomes a little less precise but I think using an 8R resistor will work well for most cells.
4.20=510mA
4.00=500mA
3.80=490mA
3.60=480mA

All those currents are similar enough to say it’s a 0.5A current on the cell. So a 4.20V open circuit voltage - 3.80V under 0.5A load voltage. So 0.40V decided by 0.5A is 800 milliohms of DC IR. That is very very bad. Of course the numbers you see in your setup right now wouldn’t be accurate due to the high resistance of those cheap cell holders and the thin wire.

If you think you can rely on the resistance readings of chargers like the Opus or the Xtar I’d say they are ok but nowhere near accurate. They use the 2 wire method and a small charge current to calculate DC IR which is inherently flawed. To measure DC IR you just use the 4 wire method which means you can’t use the voltmeter on your ZB2L3. You need to have a voltmeter AT THE TERMINALS reading cell voltage.

*Also the opus manual says to add 30mR to the reading. The Xtar VC8 gives me pretty good readings if I push the slider of the negative contact forward when I put in the cell. This is best done at storage voltage and won’t allow the IR to be measured near full because it uses a charging current that would overcharge the cell. The Xtar VC4SL and VC4S+ offer decent readings, usually a bit higher than the VC8. Occasionally the VC8 reads a bit optimistic, numbers so low they shouldn’t be possible.

[MohaModzClipzOfc]

is it safe to discharge till it reaches 2.5v???

[taketimetoheal-naturally]

nice job. thanks for sharing that :) . I use the flat top 18650 for self heating massage stones, and would love to know if anyone has a suggestion on batteries/brand? that have tested well. I just got sad when I saw the crap 9900 mah ones tested, i just bought some of those. THANK YOU for the info to avoid the ridiculous claimed ones.

[ElectronicLab.]

In this video I test some 18650 batteries

[bobbys]

How do you test a battery for its maximum discharge (CDA) 18650 without overheating or destroying the cell. Some Samsung batteries are stamped -25c but lots of cells are not. I have yet to see video that shows how they can perform a High Drain test without overheating or destroying the cell

[andyb]

That was a vey interesting and informative video, thank you. I noticed that the resisters in your link are 100 watt resisters and the one on your tester is a 50 watt. Are they supposed to be 50 or 100? I'm buying the tester from the link and was wondering if you have a diagram of how you wired the resister(s) to the tester. I guess the higher the wattage the better, just an 8 ohm resister. Thank you.

[williamsteendam]

y discharge to 2.5 v??? should discharge to 3 v

[rene]

How did you make the capacity tester ????

[JoseEarthDolera]

How did you make you capacity tester bro pls share to us. Thank you

[DumbSquirrel]

im here for knowledge not music blaring in my ear wtf good video just not the back ground