A high state of charge (SOC), particularly near or at 100%, negatively affects battery lifespan by accelerating battery degradation. Several studies and expert sources confirm this relationship for lithium-ion batteries, which are commonly used in electric vehicles (EVs) and portable electronics.
How High SOC Affects Battery Lifespan
- Faster Degradation at High SOC: Batteries kept at high SOC for extended periods tend to degrade more quickly, even when not in use (calendar degradation). This is because elevated voltages at high SOC stress the battery’s chemistry, leading to capacity loss over time.
- Reduced Cycle Life: Cycling a battery to 100% SOC and then discharging to low levels leads to greater capacity loss compared to cycling within a narrower SOC range. For instance, cycling between 85% and 25% SOC offers longer battery life than full charges to 100% followed by deeper discharges. Cycling in a modest SOC window (e.g., 75% to 65%) can dramatically extend cycle life, although it also limits usable capacity.
- Voltage and Temperature Effects: High charge voltages at full SOC combined with elevated temperatures accelerate battery degradation. High SOC typically means the battery voltage is higher, and when combined with heat, these conditions promote faster chemical breakdown inside the battery.
- Lithium Plating: At high SOC, especially when charging rapidly, lithium plating (formation of metallic lithium on the anode) can occur. This reduces the cyclable lithium available, decreasing battery capacity and lifespan. Lithium plating is a key mechanism of capacity loss in lithium-ion batteries under high SOC and fast charging conditions.
- Manufacturer Recommendations: Many manufacturers and battery management systems aim to avoid maintaining batteries at very high SOC for long periods to preserve battery health and extend lifespan. For example, keeping SOC below 80% when possible is advised to mitigate degradation.
Summary
| Factor | Effect of High SOC |
|---|---|
| Battery voltage | Increased at high SOC, stresses battery chemistry |
| Calendar degradation | Faster when battery is held at high SOC |
| Cycle life | Reduced when frequently charged to 100% SOC |
| Capacity loss | Accelerated due to lithium plating and high voltage |
| Thermal effects | Amplify degradation at high SOC |
Maintaining a high SOC, especially close to or at 100%, generally shortens battery lifespan through accelerated chemical degradation and capacity loss. Limiting maximum charge to around 80-85% and avoiding prolonged high SOC exposure can significantly improve the longevity and health of lithium-ion batteries.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-high-state-of-charge-affect-battery-lifespan/
