Do Lithium-Ion Batteries Need to Be Fully Discharged Before Charging?

When managing the charging cycle of lithium-ion (Li-ion) batteries, it is often a common question whether these batteries should be fully discharged before recharging. Surprisingly, frequent full discharges can negatively impact the longevity and overall performance of Li-ion batteries. In this article, we will explore the optimal practices for charging and discharging Li-ion batteries, the role of battery management systems (BMS), and a real-world case study.

Understanding Optimal Discharge Levels

Lithium-ion batteries are designed to perform optimally when they are kept within a range of 20-80% charge capacity. Frequently discharging them to 0% can lead to premature degradation of the battery. This is because the repeated stress of going from a full charge to a complete discharge and back can accelerate the deterioration of the battery's internal components.

What Actually Happens During Charging and Discharging?

Lithium-ion batteries have a built-in misconception where users often believe that bringing a battery to 0% is beneficial. However, frequent deep discharges can be harmful. Instead, it is recommended to charge and discharge batteries in partial cycles, so the battery stays mostly within the 20-80% charge range.

Role of Battery Management Systems (BMS)

Most modern devices equipped with Li-ion batteries include advanced battery management systems (BMS) that help optimize the charging and discharging processes. These systems prevent damage from overcharging or deep discharging, which can harm the battery over time.

Practical Example: Cycling and Urban Mobility

A notable example of efficient battery usage can be seen in an individual who uses a lithium-ion battery in an electric velomobile. This person charges and discharges their 52V 24Ah battery when the voltage drops to 50V, which means the battery is roughly at 35% charge. A smart charger, such as the Cycle Satiator used in this setup, is configured to charge the battery to 85-90% capacity (around 56.5V) and shut off when the voltage is sufficient.

In a specific instance, the author of this example pushed the battery management to its limits by attempting to use the smallest amount of power to get home, riding at a higher speed (20-22mph) while using regenerative braking to maintain a lower speed. The result was surprising, with the battery showing minimal discharge (only 0.1 volt) to travel 8 miles. Normally, a full charge (around 1.5 volts) would have been required for the same ride.

Conclusion

In summary, it is not necessary to fully discharge a lithium-ion battery before charging it. In fact, frequent full discharges can be damaging to the battery's health over time. It is best to keep the battery within a 20-80% charge range through partial discharges and recharge cycles. Utilizing a battery management system can help optimize charging and discharging, ensuring the longevity of your Li-ion battery.

Key Takeaways:

Lithium-ion batteries perform optimally between 20-80% charge. Deep discharges should be avoided to prolong battery life. Battery management systems can help optimize charging cycles. A balanced charging and discharging routine is crucial for Li-ion battery health.