Battery Degradation

Battery degradation is the gradual, irreversible loss of an EV battery's energy storage capacity and power delivery capability over time. As a battery ages and goes through charge-discharge cycles, chemical changes within the cells reduce the total energy the battery can hold.

How It Works

Degradation occurs through two primary mechanisms:

1. Calendar aging: Chemical reactions that occur simply over time, regardless of use. Heat accelerates this process.
2. Cycle aging: Wear from repeated charging and discharging. Deeper discharge cycles and frequent fast charging contribute more than shallow cycles and slow charging.

The Battery Management System (BMS) actively mitigates degradation by controlling charge rates, maintaining cell balance, and managing thermal conditions. The usable buffer the manufacturer reserves at the top and bottom of the battery also protects against the most damaging charge states.

Why It Matters

Battery degradation directly affects an EV's range over its lifetime. A vehicle that started with 400 km of range might have 340–360 km after 8 years — noticeable but manageable for most owners.

Modern EV batteries are far more durable than early concerns suggested. Most manufacturers warrant the battery to retain at least 70% capacity after 8 years or 160,000 km. Real-world data consistently shows degradation rates better than warranty thresholds.

Factors That Accelerate Degradation

• Frequent DC fast charging (minor impact with modern batteries)
• Regularly charging to 100% (NMC batteries; less relevant for LFP)
• Leaving the battery at very high or very low SoC for extended periods
• Exposure to extreme heat
• Very high mileage with deep discharge cycles

Common Values

• Typical degradation: 1–3% per year
• After 8 years: 80–92% capacity remaining (varies by chemistry and use)
• Warranty threshold: typically 70% capacity at 8 years / 160,000 km
• LFP batteries generally degrade slower than NMC for cycle-related wear