State of Health (SOH) is the single most important metric for any electric vehicle owner to understand. It represents the current maximum capacity of your battery compared to when it was new.
Why SOH Matters
Think of your EV battery like a fuel tank that slowly shrinks over time. When you buy a car with a 60kWh battery, it can hold 60kWh of energy. As the battery degrades, its capacity might drop to 54kWh. In this case, your SOH would be 90%.
A lower SOH means:
- Reduced driving range
- Potentially slower charging speeds
- Lower resale value
How SOH is Calculated
SOH is a complex calculation that involves measuring the battery's internal resistance, voltage response, and total energy output during a discharge cycle. While your dashboard might show a "100%" charge, that 100% refers to the current available capacity, not the original design capacity.
What is a "Good" SOH?
Generally speaking:
- 95-100%: Excellent condition (New to 1-2 years old)
- 90-95%: Good condition (2-4 years old)
- 80-90%: Average degradation (4-7 years old)
- Below 80%: Significant degradation
- Below 70%: Often the threshold for warranty replacement
