Keeping a battery at a high state of charge (SOC) over a long period leads to several detrimental effects that accelerate battery degradation and reduce its overall lifespan:
- Increased Stress and Capacity Loss: Maintaining a battery at a high SOC, especially near full charge (close to 100%), causes more stress on the battery’s internal chemistry compared to staying at moderate charge levels. This stress accelerates capacity loss, reducing the amount of charge the battery can hold over time.
- Voltage-Related Degradation: High SOC corresponds to a higher voltage within the battery cells (for lithium-ion batteries typically above 4.1 V per cell). Prolonged exposure to this elevated voltage promotes faster chemical degradation and loss of active materials inside the battery.
- Temperature Interaction: The negative effects of high SOC are compounded by temperature. When stored or kept at high charge and simultaneously exposed to elevated temperatures (e.g., 40°C or more), the battery undergoes a more rapid decline in capacity. For example, a lithium-ion battery stored fully charged at 25°C can lose about 20% capacity after one year, but at 40°C under full charge, the loss can reach 35% or more.
- State of Health (SOH) Decline: Over time, the combination of staying at high SOC and frequent cycling at high voltages decreases the battery’s SOH, meaning the effective usable capacity is reduced compared to the capacity when new.
- Safety Risks: Batteries kept at or above high SOC percentages for extended periods have an increased risk of thermal runaway, which can cause overheating, fire, or release of toxic gases, especially in lithium-ion chemistries if the battery is stressed or damaged.
In summary, to maximize battery life and minimize degradation, it is advisable to avoid keeping batteries at full or near-full charge levels for prolonged periods, especially in warm environments. Partial charges and storage at moderate SOC levels (around 40-60%) significantly slow down capacity loss and enhance longevity.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/what-are-the-effects-of-keeping-a-battery-at-a-high-state-of-charge-over-a-long-period/
