State of Health
Also known as: SOH, health estimation
State of Health (SOH) quantifies battery degradation by measuring how much capacity and power capability have been lost due to aging. SOH is expressed as a percentage (100% = new, 80% = end of life for many applications). Tracking SOH enables predictive maintenance, end-of-life detection, and accurate range/power predictions in aging systems. SOH reflects cumulative effects of cycling, calendar aging, and operating conditions.
Key highlights
- Captures real, irreversible battery degradation
- Enables predictive maintenance and end-of-life detection
- Provides actionable information for operation optimization
- Can be combined with SOC for comprehensive battery state assessment
Intuition
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How it works
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When to use it
Use SOH estimation in electric vehicles, renewable energy storage systems, and battery packs with significant economic value. It is essential for warranty management, second-life applications, and battery replacement timing. Avoid relying on SOH estimates when cycling patterns or operating temperatures are highly variable and unpredictable.
Strengths & limitations
- Captures real, irreversible battery degradation
- Enables predictive maintenance and end-of-life detection
- Provides actionable information for operation optimization
- Can be combined with SOC for comprehensive battery state assessment
- Direct measurement requires full discharge tests (time-consuming, stressful)
- Estimation from indirect indicators (voltage, resistance) has uncertainty
- Degradation mechanisms interact in complex ways, hard to model accurately
- Historical data may not predict future degradation under changed conditions
Common pitfalls
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Applications
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Frequently asked
How is SOH measured in practice?
Direct measurement: perform controlled discharge from 100% to 0% SOC at constant current, measure total charge delivered. SOH = Q_measured / Q_rated. Indirect estimation: use regression based on cycle count, temperature history, and voltage/resistance measurements. Direct is accurate but stressful; indirect is practical for real-time monitoring.
What temperature effects should I consider for SOH?
Degradation accelerates exponentially with temperature, approximately doubling for every 10°C increase. Cold storage (0-5°C) slows aging; warm storage (35°C+) accelerates it. Combined cycling at elevated temperature degrades much faster than cycling at moderate temperature. SOH models should include temperature-dependent aging rates.
Can I predict remaining useful life from SOH trend?
With caution. If you have 6+ months of SOH trend data showing steady decline rate, you can project when SOH reaches 80% (typical end-of-life). However, degradation often accelerates near end of life, and changed operating conditions (temperature, charge rate) can alter trajectory. Use SOH projections for planning, not for critical decisions.
Sources
- 1.Birkl, C. R., Roberts, M. R., McTurk, E., Bruce, P. G., & Howey, D. A. (2017). Degradation diagnostics for lithium ion cells. Journal of Power Sources, 341, 373-386.
- 2.Xiong, R., Sun, F., He, H., & Gong, X. (2018). Online estimation of widespread existence of unmodeled dynamics in lithium-ion battery for electric vehicles. Energies, 11(8), 1943.
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Cite this page
ScholarGate. (2026, June 3). State of Health. ScholarGate. https://scholargate.app/thermodynamics/state-of-health