Used EV Buyer's Guide: How to Check Battery Health and Degradation

Electric vehicles (EVs) are simpler mechanically than internal combustion engine vehicles, with fewer moving parts to break. However, they contain one massive, expensive component that dictates the vehicle's entire lifespan: the high-voltage battery pack. If you are buying a used EV, understanding battery health is the absolute most important step.

What is Battery Degradation?

Just like smartphone batteries, EV batteries slowly lose their maximum charge capacity over time and usage. A typical EV battery degrades at a rate of 1% to 2% per year. However, poor charging habits, extreme heat, and high mileage can accelerate this degradation, leaving a used EV with significantly less range than its original specs.

How to Check State of Health (SOH)

State of Health (SOH) represents the remaining battery capacity as a percentage of its original factory capacity. Here is how to check SOH before buying:

• Dashboard Diagnostics: Some EVs show battery health directly. For example, older Nissan Leafs have a bar indicator on the dash. Teslas have a hidden Service Menu where you can run an automated battery health test.
• Use an OBD2 Scanner: Connect an OBD2 scanner to the vehicle's port and use specialized apps (like LeafSpy for Nissan, OBD Ampehre for Chevrolet, or Car Scanner ELM OBD2) to read the exact battery cell voltages and SOH values directly from the Battery Management System (BMS).
• Conduct a Range Test: Charge the vehicle to 100% and drive it. Note the odometer reading and state of charge to calculate the actual energy capacity of the battery under real-world driving conditions.

Factors that Damage EV Batteries

Review the vehicle's history to see if it was subjected to battery-degrading environments:

• Excessive DC Fast Charging: High-power fast charging heats the battery, causing stress on the internal lithium-ion chemistry. Consistent home charging (Level 2) is much healthier.
• Extreme Climates: High ambient temperatures accelerate chemical degradation. EVs stored in hot states like Arizona degrade faster than those in cooler climates.

Understanding EV Battery Warranties

In the US, federal regulations mandate that EV battery warranties cover at least 8 years or 100,000 miles (California extends this to 10 years or 150,000 miles). Most manufacturers guarantee the battery will not drop below 70% capacity during this period. Verify if the battery warranty is still active and transferable to you as the new owner.

Conclusion

An EV with a degraded battery is not necessarily a bad purchase – it can be a great bargain if you only need the car for short commutes. However, ensure the purchase price reflects the battery's SOH. Checking battery health protects you from inheriting a vehicle that requires a costly battery pack replacement.