1. From the appearance size, 18650 battery, diameter of 18MM, height of 65MM, can be measured by caliper specific size
2. Visual inspection of its appearance and PVC, quality color can distinguish its quality; However, it is difficult to tell whether a lithium battery is good or bad just by looking at it
3. Multimeter to measure its voltage, there are a lot of batteries on the market, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide and other cathode materials of the battery, the voltage is 3.7V, 3.2V, 3.6V, each has its own advantages.
4. If there is an internal resistance meter, you can also detect the internal resistance.
