Power Bank Battery Cycle Life: Does Deep Charge and Discharge Really “Activate” the Battery?

In our daily lives, power banks have become an indispensable “power source,” continuously supplying electricity to various electronic devices. However, many questions about the battery cycle life of power banks, such as whether deep charge and discharge are beneficial for battery activation and the pros and cons of long-term storage in a full-charge state, have always puzzled consumers. Today, let’s delve into the truth behind these questions.

1. Laboratory Teardown: Expansion of Lithium-Polymer Cells After 500 Cycles

• Rigorous Experimental Process: In a professional laboratory setting, a set of high-quality lithium-polymer cell samples were selected for high-load deep charge and discharge cycle testing. After 500 cycles, with each cycle precisely controlled to charge to 100% and then fully discharge to automatic shutdown, simulating extreme usage scenarios for ordinary users.
• Expansion and Impact Analysis: The experimental results showed that the lithium-polymer cells exhibited a certain degree of expansion. The thickness of the cells increased by approximately 8% compared to their initial state. This is mainly because during deep charge and discharge, lithium ions shuttle intensely between the cathode and anode, causing gradual changes in the microstructure of the electrode materials. For instance, lithium deposition occurred in graphite anodes, and the layered structure of the cathode material collapsed. These changes led to electrolyte decomposition and gas generation, causing cell expansion. Cell expansion can not only disrupt the internal structure of the power bank and affect its appearance, but also pose safety hazards such as internal short-circuits and overheating. Moreover, it significantly reduces the battery’s capacity retention rate and shortens its effective service life.

2. BMS Board Lock-Electricity Strategy: Software Shows 0% but 30% Power Remains

• BMS Board Lock-Electricity Strategy Unveiled: The BMS (Battery Management System) board inside the power bank adopts a “lock-electricity” strategy to safeguard battery life and safety. When the power bank displays 0% power, the cell’s power is not actually fully depleted, with about 30% remaining but unused. Based on preset complex algorithms and protection mechanisms, the BMS system restricts deep discharge of the cell to prevent excessive voltage drop and irreversible damage.
• Impact on Battery Life and Safety: In the long run, the BMS board’s lock-electricity strategy acts like a “guardian angel,” effectively prolonging the cell’s cycle life. Over-discharge can cause the cell’s electrolyte to dry up and electrode materials to powder, leading to rapid performance degradation. By locking electricity, the cell retains a relatively safe minimum charge after each discharge, maintaining the internal chemical system’s stability. This reduces structural damage caused by over-discharge and allows the cell to repeatedly charge and discharge in a relatively healthy state, providing users with continuous and stable power support.

3. Maintenance Misconception: Long-Term Storage in Full-Charge State Accelerates Aging

• The Harm of Full-Charge Storage: Many users are accustomed to storing power banks in a full-charge state in drawers or cabinets, thinking they can be used at any time with sufficient power. However, this practice actually accelerates the aging of lithium-polymer cells. When fully charged, the internal electrode materials of lithium-polymer cells are in a high oxidation-reduction potential state, highly active and unstable. Over time, even without charging or discharging operations, side reactions within the cell remain active, such as spontaneous lithium ion intercalation and slow electrolyte decomposition. These processes gradually reduce battery capacity and increase internal impedance.
• Scientific Storage Suggestions and Experimental Data Support: Test data from professional organizations indicate that long-term storage of power banks in a full-charge state reduces capacity retention by about 5% – 8% per month. In contrast, storing the power bank with its charge maintained between 40% – 60% lowers the monthly capacity decay rate to 1% – 3%. Therefore, it is advisable for users to charge or discharge their power banks to around 40% – 60% every 3 – 6 months during storage. This practice maximizes the delay of cell aging and ensures the power bank has ample power when needed.

4. Revival Experiment: Success Rate of Battery Balancers in Repairing Over-Discharged Batteries

• Hazards of Over-Discharged Batteries and Repair Principle of Battery Balancers: When power bank cells are over-discharged, the internal electrode material structure and electrolyte composition become disordered. Excessively low voltage prevents lithium ions from embedding normally in the electrode material, and numerous irreversible chemical reactions occur within the battery, causing the cell to “hibernate” and making it unresponsive to conventional charging methods. Battery balancers can repair over-discharged batteries by applying precise low-voltage pulses to the cell, gradually reactivating the cell’s active substances. This process prompts lithium ions to re-establish ordered intercalation and deintercalation pathways between the cathode and anode, restoring the cell’s basic electrochemical performance.
• Experimental Success Rate and Limitations Analysis: Extensive experiments have shown that the success rate of battery balancers in repairing over-discharged batteries is not absolute. For mildly over-discharged cells (voltage above 2V) with a short duration (1 – 2 weeks), the repair success rate can reach 70% – 80%. However, for deeply over-discharged cells (voltage below 1V) that have been left unused for an extended period (over 1 month), the success rate plummets to 10% – 20%. Long-term deep over-discharge severely damages the cell’s internal physicochemical structure, making it difficult for even battery balancers to restore its performance. Therefore, in daily use, it is essential to avoid over-discharging power banks and to follow correct usage guidelines. This is the fundamental way to ensure cell health.

In today’s world where power banks are becoming increasingly popular, understanding the key aspects of power bank battery cycle life is highly valuable for our daily use. Deep charge and discharge is not a “magic pill” for battery activation and may instead pose hidden dangers; the BMS board’s lock-electricity strategy is designed to protect battery life. Scientific storage and timely, proper charging habits are the only ways to extend the battery life of power banks. Only by dispelling these misconceptions can we ensure that power banks remain by our side, continuously injecting vitality into our electronic devices.