How to judge whether the lithium ion battery is bad?

First, check what type of lithium battery it is and try to find the manufacturer's specifications. This is the best way to find out the performance of a particular battery in terms of voltage limits, current, internal resistance, etc.

Then-try to measure (if you have tools or know how to do it) voltage, resistance and performance. Compare these values with the manufacturer's specifications. Match? Still far away? It's that simple.

If your measurements are more or less consistent with the manufacturer's claims, it should be fine.

If this is not the case, it may be safer to discard this battery. It is not worth the risk of fire or similar.

If the manufacturer's data is not available, then try to find out what kind of lithium battery (battery) it is, and then measure based on it. There are many different types (the three most common lithium rechargeable batteries are >> nominal voltage 3.6V lithium ion batteries, 3.2V LiPO4 batteries, 2.4V LTO batteries, etc.)

To determine whether a lithium battery is bad, the easiest way is to charge it to a fully charged state (close to 100%), and then measure the voltage drop during discharge.

Example: 18650 battery, rated capacity 2600mAh, nominal voltage 3.6V, fully charged 4.2V, cut-off discharge limit 2.75V. Charge to about 4.1–4.2V, then start discharging with 1A current. At this time, the voltage drop is measured. It should not fall below 4 volts. If it is lower than 3.9, 3.8 or lower, the battery is very old and can be packed at any time.

In addition, if this battery (as described above) is overheated during charging/discharging 1A, it is not safe to use it again, it is best to discard it.

And the speed of self-discharge can tell you whether the battery is good or bad. Fully charged and placed in a safe place. Read the voltage after a few hours. note. After one month (or even two months), measure the voltage again. The difference from the first measured value should not exceed 10% of the total value. If it is bad.