How to Determine if a 18650 Lithium Battery Has Failed?

How to Determine if a 18650 Lithium Battery Has Failed? ---- Identifying Swelling, Leakage, and Overheating

18650 lithium-ion batteries are used in various applications, including laptops, power tools, 

and electric vehicles. However, like all batteries, they have a limited lifespan and may fail over 

time due to aging, overuse, or improper handling. Identifying a failed or failing 18650 battery 

is crucial to ensure safety and maintain device performance. Here are the key indicators to 

determine if an 18650 battery has failed:

1. Swelling (Bulging or Puffing)

One of the most visible signs of a failing 18650 battery is swelling. If a battery appears deformed 

or its casing is bulging, this indicates internal gas buildup due to chemical reactions inside the cell. 

Swelling can occur due to overcharging, deep discharge, or exposure to high temperatures. 

A swollen battery is dangerous and should not be used, as it may rupture or explode.

2. Leakage

Battery leakage is another serious issue that signals failure. If you notice any liquid or white 

powdery substance oozing from the battery, this indicates electrolyte leakage. Leaked electrolytes 

are corrosive and can damage electronic components, posing safety hazards such as short circuits or 

fire risks. Leaking batteries should be handled with care and disposed of properly according to 

environmental regulations.

3. Overheating

While lithium-ion batteries naturally generate heat during charging and discharging, excessive 

heating is a warning sign of failure. If an 18650 battery becomes abnormally hot to the touch 

even during normal use or charging, it may indicate an internal short circuit, overloading, or 

degradation of internal components. Overheated batteries pose a fire risk and should be replaced 

immediately.

4. Voltage and Performance Drop

A significant decrease in battery capacity or inability to hold a charge is a clear indication of failure. 

If a fully charged battery drains rapidly or does not power a device as expected, it may have deteriorated. 

Using a multimeter to measure voltage can help confirm this; a healthy 18650 battery typically holds 

around 3.7V to 4.2V when fully charged. A voltage reading far below the nominal level suggests a failing cell.

5. Internal Short Circuit or Unusual Smell

If a battery emits a burnt or chemical odor, it may have experienced an internal short circuit or severe 

electrolyte degradation. This is a critical failure sign, and such batteries should be discarded immediately 

to avoid safety risks.

Conclusion

Regularly checking your 18650 batteries for signs of swelling, leakage, overheating, or performance decline 

is crucial for safety. If you notice any of these issues, stop using the battery immediately and dispose 

of it properly. To prevent premature failure and potential hazards, always store and charge batteries in a controlled environment.