This is the equipment I use for cell testing:
West Mountain Radio CBA IV Pro battery analyzer, modified for low voltage drop . Accuracy = +/-1% up to 20A.
Custom constant-current electronic load, rated 150A/400W. Accuracy = +/-0.6% up to 150A. A second load is available, if not being used for other testing, if I need to discharge at over 150A (up to 300A).
Adjustable 5A/30V CC/CV power supply for charging the cell.
Omegaette HH308 dual type-K thermocouple thermometer. Accuracy = +/-0.3% + 1C.
20A, 100A, and 200A current measuring shunts. Accuracy = +/-0.25%.
Fluke 8846A 6-1/2 digit DMM. Accuracy better than +/-0.01%.
Low-resistance cell clamping rig.
Safety glasses, fire-resistant apron, fire-resistant gloves. I wear all when doing destructive testing or if I think the cell temperature will rise much above 100°C. Otherwise just the safety glasses.
The CBA battery analyzer handles 10% of the discharge current and creates the graphs. The custom load handles 90% of the current.
The cell has its wrapper removed so the thermocouple can be placed directly against the metal can to sense temperature.
The thermocouple, plus 0.5" of its cable (to prevent ambient air from cooling it and affecting the thermocouple), are tightly Kapton-taped to the cell with the thermocouple positioned halfway down the cell.
All discharges, unless noted, are constant-current to within +/-1% of the stated value. Confirmed via +/-0.25% tolerance current shunt.
All measured temperatures were rounded to the nearest degree-C. Only the highest temperature for the discharge is recorded.
The cell is placed in an insulated fireproof container with a lid loosely placed on top. The container is left open at the top to allow heat to escape during discharge. If a cell vents the cover is closed and a fan is turned on to evacuate the gas/vapor outside via a flexible metal hose.
The cell holder is a non-conductive c-clamp using a 1" x 1", 0.040" thick copper plate to connect to the bottom of the cell. A 1/4" diameter copper rod is used to connect to the top of the cell. Both the top and bottom connections have 10AWG and 12AWG silicone-insulated wires soldered to them. The 10AWG wires go to the 400W load and the 12AWG wires go to the CBA, directly soldered to the CBA circuit board. I do not use the CBA's PowerPole connectors as their resistance is too high.
Why only a 1/4" copper rod for the top of the cell? One reason is that's the equivalent of 3AWG wire...plenty beefy enough. The other reason is that I don't want to conduct any more heat from the cell than I have to.
The performance of a cell over months of use in our devices doesn't just depend on that how that cell does for one or two discharges when new. It depends on how fast the cell ages over time.
What affects this aging? Assuming you're not overcharging or overdischarging, temperature has the biggest effect on your battery's health. The hotter you run them, the quicker they will start to lose capacity and run at a lower voltage.
To better determine how a cell will perform over time I run multiple discharges at the cell's specified or accepted continuous discharge rating (CDR). If the cell gets too hot, much over 75°C, then I know that the CDR rating is too high for that cell. I then run another lower-current discharge to measure the capacity loss and damage that the high temperatures might have caused. If there was a capacity loss then I have confirmation that running at the cell's specified CDR is harmful. This means that the CDR needs to be lowered.
When picking a CDR I'll select the discharge current level that results in the cell temperature rising no higher than approximately 75°C. While this is an extraordinarily high temperature to operate a cell at, it does allow for powering the small devices we use now while still maintaining decent battery life and safety margins.
If you see test results elsewhere that rate a cell a lot higher, or lower...ask questions! What temperatures did the cell reach during testing? Did the tester do multiple discharges to see if the cell started to show signs of damage at its CDR? What method did the tester use to measure temperature? Some popular methods are very poorly suited for measuring cell temperatures.
All these questions may seem overly geeky but the answers will make you a better, safer vaper and help you to pick the tester(s) you trust to review the cells you're putting up to your face.
Another question might be, why do I say "cell" instead of "battery"?
To prevent confusion with the portion of a vaping device that powers the coil, often (confusingly) called a "battery", I use the term "cell". It's also the term used by cell manufacturers and my clients so I'm just used to it.
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