SOH

State of Health (SOH) is a pivotal technical benchmark used to evaluate the ageing and degradation levels of a high-voltage (HV) battery pack, energy storage system, or fuel cell. In the electric vehicle (EV) sector, SOH is quantitatively expressed as a percentage (%), benchmarking the traction battery's current maximum usable capacity or remaining health against its original factory-fresh condition. A brand-new battery typically registers an SOH of 100% (or slightly higher). Over time, as mileage accrues, charge-discharge cycles accumulate, and the pack endures harsh operational environments such as tropical heat and frequent DC fast charging, the SOH progressively deteriorates. Once the SOH drops below a specific critical threshold (typically between 70% and 80%), overall battery performance and real-world driving range decline drastically, signalling the need for specialised maintenance or an outright battery replacement.

Core Technical Architecture and Working Principles

SOH cannot be directly measured via a single physical sensor; instead, it is derived via advanced algorithmic models running on the Battery Management System (BMS), relying on long-term data logging and comprehensive estimation: 

Multi-Dimensional Electrochemical Parameter Acquisition and Ampere-Hour Integration:

The BMS continuously tracks the battery's open-circuit voltage (OCV), internal resistance dynamics, charge/discharge currents, and operating temperatures throughout its entire operating life. Through Coulomb counting (ampere-hour integration), the core algorithm tracks the net charge throughput across every charge cycle in real time. Paired with the rise in dynamic internal resistance (where higher internal resistance reflects advanced cell ageing), the BMS dynamically recalculates the battery's current maximum usable capacity. 

Big Data Deep Learning and Multi-Condition Correction Algorithms:

Modern SOH estimation setups go beyond on-board BMS processing by incorporating cloud-based fleet telematics for in-depth calibration. The system automatically filters out short-term fluctuations caused by shallow charging habits or ambient parking temperature shifts. It isolates the irreversible capacity fade stemming from cathode lattice collapse, electrolyte depletion, and lithium plating on the anode, delivering an exceptionally precise SOH readout. 

Safety Specifications and Physical Limitations

Strictly Prohibit Sustained High-Load Long-Distance Driving When Traction Battery SOH Has Severely Degraded (e.g. Below the 70% Critical Threshold), Shows Exceptionally High Internal Polarisation Resistance, and Suffers from Noticeable Parasitic Drain or Abrupt Drops in Charge State: 

A battery pack with an exceptionally low SOH suffers from compromised internal integrity, marked by advanced physical degradation and the risk of latent micro-short circuits. Battery ageing alerts must never be ignored. Under high-current draws or inputs (such as hard acceleration or high-output DC rapid charging), degraded cells generate excessive heat, drastically elevating the risk of thermal runaway and catastrophic fire hazards. 

Strictly Prohibit the Tampering with, Resetting, or Masking of Genuine Battery SOH Data via Unauthorised Diagnostic Tools or Firmware Flashing to Mislead Buyers During Used EV Transactions or Pre-Purchase Inspections: 

The true health of an EV battery directly dictates vehicle roadworthiness and resale value. Fabricating an artificial 100% SOH reading through third-party flashing utilities is strictly prohibited. Concealing severe battery degradation not only deceives buyers, but also strips the vehicle of its built-in safety safeguards, posing serious safety risks on the road.