Understanding State of Health (SOH): A Key Metric for Electric Vehicles

When considering the longevity and performance of an electric vehicle (EV), State of Health (SOH) is an essential metric. It provides an accurate snapshot of your EV battery’s health, indicating how much usable energy it can store compared to its original capacity when it was new.

What is State of Health (SOH)?

SOH is a percentage that measures the current capacity of your EV battery relative to its original capacity. Think of it as a “battery health report.” For example, if your battery’s SOH is 80%, it means it can only store 80% of the energy it could when it was new, indicating some degree of degradation.

• Higher SOH: The battery is in good condition and can hold most of its original capacity.

• Lower SOH: The battery has experienced wear and can hold less energy, leading to shorter range and reduced performance.

Why is SOH Important?

• Range & Performance: A higher SOH means the battery can store more energy, which results in longer driving range and better performance. As SOH drops, range decreases, and performance may become sluggish.

• Battery Lifespan: SOH offers insights into how much life your EV battery has left. While modern batteries are designed to last between 8-15 years, their capacity naturally declines over time. For example, an EV battery may lose 20%-30% of its capacity after 8-10 years of use under normal conditions.

• Resale Value: A higher SOH can boost your EV’s resale value. Prospective buyers or dealerships are more likely to pay a premium for a vehicle with a battery in good health, as it suggests the vehicle has more life left.

Factors Affecting SOH

Several factors contribute to the degradation of an EV battery and affect its SOH:

1. Temperature Extremes:

   • Hot Weather: Excessive heat can cause internal chemical reactions that shorten the battery’s lifespan.

   • Cold Weather: Low temperatures can reduce the battery’s efficiency and cause it to lose capacity faster.

   • Tip: Parking in a garage or shaded areas can help protect the battery from extreme temperatures.

2. Charging Habits:

   • Frequent Full Charges: Charging your battery to 100% regularly can stress the cells.

   • Deep Discharges: Running your battery all the way to 0% can also lead to degradation over time.

   • Tip: Keep your battery level between 20% and 80% for optimal health.

3. Driving Style:

   • Aggressive Driving: Rapid acceleration and hard braking can increase stress on the battery, accelerating degradation.

   • Tip: A smooth driving style with gradual acceleration and deceleration can help maintain battery health.

4. Charging Speed:

   • Fast Charging: Frequent use of rapid chargers can lead to higher internal resistance in the battery, contributing to faster degradation.

   • Tip: Use slow charging for routine daily use and reserve fast charging for longer trips when needed.

Monitoring SOH

Modern EVs often come equipped with battery management systems (BMS) that continuously monitor SOH and provide real-time data. You can typically access this information through:

• The vehicle’s infotainment screen.

• A dedicated mobile app (e.g., Tesla, Nissan Leaf, BMW i3 apps).

• Diagnostic tools: Some third-party apps and services, such as Moba Certify Pro, offer a more detailed SOH analysis and a certificate for tracking battery health over time.

Many EVs also allow you to monitor cycle count (number of charge cycles), which is closely tied to SOH.

Maximizing EV Battery Life

To extend your EV battery’s life and maintain its SOH, here are some best practices:

1. Moderate Charging: Avoid consistently charging your EV to 100%. Instead, keep the charge between 20%-80% for most daily driving needs.

2. Temperature Control:

   • Hot weather: Park in shaded areas or garages to protect the battery.

   • Cold weather: Use a garage or car cover to shield the battery from freezing temperatures.

3. Regular Maintenance: Follow the manufacturer’s maintenance guidelines to ensure proper care and function of the EV battery and charging system.

4. Avoid Extreme Charging Conditions: Charge your EV when it’s neither too hot nor too cold. Using a fast charger is fine occasionally but should not be the primary charging method.

Recent Developments in SOH Testing

• Advanced Diagnostics: Companies like Moba now offer tools such as Moba Certify Pro to assess SOH with greater accuracy, ensuring you get an objective, detailed report. These solutions provide a digital certificate that can be used for warranty claims or resale, giving you a clear view of battery health.

• SOH Monitoring and Updates: With more advanced BMS systems, some EV manufacturers are adding over-the-air updates to improve battery management and offer more accurate real-time SOH data for users.

Conclusion

Understanding State of Health (SOH) is critical to getting the most out of your EV. By monitoring your battery’s SOH and following best practices for charging, temperature control, and driving habits, you can ensure that your EV delivers optimal performance and maximized longevity. Whether you’re a current EV owner or considering buying one, staying informed about SOH can help you make more sustainable and cost-effective decisions for your vehicle.