State of health

State of health (SoH) is a figure of merit of the condition of a battery (or a cell, or a battery pack), compared to its ideal conditions. The unit of SoH is percent (100% = the battery's conditions match the battery's specifications). For example, when the capacity of a new battery is same as the nominal capacity as per the battery specification, it is said to be in optimal health (SoH = 100%). As the battery is further utilized in a device, its health as in its capacity and other useful parameters deteriorate till it reaches the end of life (SoH = ~70-80%). Consequently, such batteries are replaced from regular usage pertaining to their unstable and unreliable performance.^[1]^[2]

Typically, a battery's SoH will be 100% at the time of manufacture and will decrease over time and use. However, a battery's performance at the time of manufacture may not meet its specifications, in which case its initial SoH will be less than 100%. In the domain of electric vehicles, the biggest factors that contribute to battery degradation are driver patterns, driver aggression, climate, cabin thermal dynamics, and infrastructure, with driver patterns and climate being the biggest.^[3]

^ Pradhan, S. K.; Chakraborty, B. (2022-07-01). "Battery management strategies: An essential review for battery state of health monitoring techniques". Journal of Energy Storage. 51: 104427. doi:10.1016/j.est.2022.104427. ISSN 2352-152X.
^ Tao, Tingting; Ji, Cheng; Dai, Jindong; Rao, Jingzhi; Wang, Jingde; Sun, Wei; Romagnoli, Jose (2024-02-01). "Data-based health indicator extraction for battery SOH estimation via deep learning". Journal of Energy Storage. 78: 109982. doi:10.1016/j.est.2023.109982. ISSN 2352-152X.
^ Neubauer, Jeremy S.; Wood, Eric; Pesaran, Ahmad (2015). "A Second Life for Electric Vehicle Batteries: Answering Questions on Battery Degradation and Value" (PDF). SAE International Journal of Materials and Manufacturing. 8 (2): 544–553. doi:10.4271/2015-01-1306. ISSN 1946-3979. JSTOR 26268745. OSTI 1215098.

[:0-1] Pradhan, S. K.; Chakraborty, B. (2022-07-01). "Battery management strategies: An essential review for battery state of health monitoring techniques". Journal of Energy Storage. 51: 104427. doi:10.1016/j.est.2022.104427. ISSN 2352-152X.

[:1-2] Tao, Tingting; Ji, Cheng; Dai, Jindong; Rao, Jingzhi; Wang, Jingde; Sun, Wei; Romagnoli, Jose (2024-02-01). "Data-based health indicator extraction for battery SOH estimation via deep learning". Journal of Energy Storage. 78: 109982. doi:10.1016/j.est.2023.109982. ISSN 2352-152X.

[3] Neubauer, Jeremy S.; Wood, Eric; Pesaran, Ahmad (2015). "A Second Life for Electric Vehicle Batteries: Answering Questions on Battery Degradation and Value" (PDF). SAE International Journal of Materials and Manufacturing. 8 (2): 544–553. doi:10.4271/2015-01-1306. ISSN 1946-3979. JSTOR 26268745. OSTI 1215098.

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