Exploring the Safe Discharge Cutoff Voltage of Lithium Batteries

During capacity tests, the discharge cutoff voltage is the lowest voltage at which a lithium battery should stop working. If the discharge cutoff voltage is set too high, the battery may not fully discharge, leading to inaccurate measurements. On the other hand, if it’s set too low, the battery could be over-discharged, which can reduce its lifespan and even cause safety issues like leakage.

Therefore, setting a correct cutoff voltage is crucial for prolonging the lifespan of lithium batteries and ensuring their safe use. Next, let’s explore the safe discharge cutoff voltage of lithium batteries commonly used in life.

The Discharge Cutoff Voltage of 3.6/3.7V Lithium Battery

A user on the BudgetLight Forum raised a question: “The data sheet for my lithium battery shows that the nominal voltage is 3.6V, the fully charged voltage is 4.2V, and the cutoff voltage is 2.5V. However, I’ve seen a lot of discussions online about battery over-discharge. Some batteries stop working when the voltage drops below the nominal voltage, while others activate protection mechanisms when the voltage falls below 3.3V. To maximize the battery capacity without damaging it, what discharge cutoff voltage should I choose?”

Lithium battery manufacturers typically set the discharge cutoff voltage for 3.6/3.7V lithium batteries between 2.5V and 3V. According to the International Electrotechnical Commission (IEC), the recommended discharge cutoff voltage for these batteries is 2.5V. If it is lower than 2.5V, it may cause the battery to be over-discharged, while setting it higher than 2.5V may affect the accuracy of capacity tests.

Taking the XTAR 16340 850mAh battery as an example, the data shows that as the cutoff voltage increases from 2.5V, the measured capacity decreases, leading to a significant difference from the nominal value. Consequently, XTAR chargers and many well-known battery reviewers usually use 2.5V as the cutoff voltage during capacity tests. This approach ensures accurate measurements while minimizing potential harm to the battery.

The Discharge Cutoff Voltage of 1.5V Rechargeable Lithium Battery

The 1.5V rechargeable lithium battery actually uses a 3.6V cell and achieves a 1.5V output through an internal step-down smart chip. As a result, the discharge cutoff voltage is determined by the internal step-down chip and cannot be directly measured by external devices.

Due to the differences in R&D technology between different brands, the discharge cutoff voltage for 1.5V rechargeable lithium batteries can vary. When using the VX4 charger for capacity testing on these batteries, the XTAR lab sets a lower cutoff voltage of 0.5V. The purpose of this is to ensure that batteries of different brands can get more accurate testing results. The reason for choosing 0.5V instead of 0V is that some unknown brands of 1.5V lithium batteries may lack an over-discharge protection. If the voltage drops to 0V, it could lead to severe over-discharge and irreversible damage to the battery.

Conclusion

Before choosing a charger for lithium battery capacity testing, it’s important to carefully understand its parameter settings. Avoid using an incorrect discharge cutoff voltage to prevent potential damage to the battery or inaccurate test results. A safe discharge cutoff voltage not only effectively protects the battery but also ensures that the battery performs at its best in practical applications.