How to calculate the “cycle times” of lithium batteries?

Understanding the calculation method of lithium battery cycle times and the influencing factors is crucial for us to correctly use and maintain lithium batteries. When using electronic devices in daily life, we should try to adopt scientific charging methods, avoid extreme temperature environments, and choose lithium battery products with reliable quality. Only in this way can we extend the service life of lithium batteries, give full play to their performance advantages, and bring more convenience to our lives and work.

I. What is the "cycle times" of lithium batteries?

The cycle times of lithium batteries refers to the complete process of the battery from full charge to full discharge and then full charge. For example, if a 3000mAh battery is used from 100% to 0% and then charged back to 100%, it is considered a complete cycle.

However, in actual use, we rarely fully discharge the battery and then charge it again. Therefore, the calculation of the number of cycles is based on the cumulative discharge amount. For example:

• If you charge after using 50% of the power each time, then two uses (50% + 50%) accumulate to 100%, which is considered a cycle.
• If you charge after using 25% of the power each time, then four uses (25% × 4) accumulate to 100%, which is considered a cycle.

 

II. The relationship between the number of cycles and battery life

The life of a lithium battery is usually measured by the number of cycles. For example:

• The times of cycles of ordinary lithium batteries is 300~500 times, after which the capacity will decay to about 80% of the initial capacity.
• High-quality batteries (such as lithium iron phosphate batteries) can reach more than 2,000 cycles.

It should be noted that the number of cycles is not an absolute life indicator. The actual life is also affected by the following factors:

1. Depth of charge and discharge (DOD): Shallow charge and discharge (such as 20%~80%) can significantly extend the battery life.
2. Temperature: High temperature (>35℃) or low temperature (<0℃) will accelerate battery aging.
3. Charging speed: Although fast charging is convenient, it will slightly shorten the battery life.

 

III. How to calculate the number of cycles?

1. Simple calculation method

Assume that the capacity of a battery is 3000mAh:

• If you use 1500mAh and charge it every day, then the cumulative use of 3000mAh in two days is counted as one cycle.
• If you use 750mAh and charge it every day, then the cumulative use of 3000mAh in four days is counted as one cycle.

2. Examples in actual applications

• Mobile phone batteries: Use 50% of the power every day and charge it, and use 100% in two days, which is counted as one cycle. About 180 cycles a year.
• Electric vehicle battery: Charge after consuming 20% of the power each time you ride, and use 100% of the power in five times, which counts as one cycle. If you ride once a day, it will be about 73 cycles a year.

 

IV. How to extend the battery life?

1. Avoid deep discharge: Try to charge when the power is less than 20% to avoid complete discharge.
2. Shallow charge and discharge: Keep the power between 20% and 80%, which can significantly extend the life.
3. Control temperature: Avoid using or charging in high or low temperature environments.
4. Use the original charger: Poor quality chargers may cause overcharge or over-discharge, damaging the battery.

 

V. Common misunderstandings

1. "Every charge counts as a cycle": Wrong! The number of cycles is based on the cumulative discharge, not the number of charges.
2. "New batteries need to be fully charged for 12 hours to activate": Outdated concept! Lithium batteries are activated at the factory and do not need to be charged for a long time.
3. "Fast charging will definitely damage the battery": Not entirely correct! Fast charging will slightly shorten the life, but the impact is limited, and there is no need to worry too much about daily use.

 

VI. Summary

The number of cycles of lithium batteries is an important indicator to measure their lifespan, but the actual lifespan is also affected by factors such as usage habits and ambient temperature. The battery life can be significantly extended by shallow charging and discharging, controlling the temperature, and avoiding deep discharge. I hope this article can help you better understand the "number of cycles" of lithium batteries and scientifically manage your device batteries!