What factors primarily determine the remaining useful life (RUL) of a battery?

The remaining useful life (RUL) of a battery is primarily determined by its current State of Health (SOH), its operating conditions, and its historical usage patterns. The State of Health (SOH) reflects the overall condition of the battery and its ability to perform as originally designed. SOH is typically expressed as a percentage, where 100% represents a new battery and lower percentages indicate degradation. The SOH is affected by factors such as capacity fade, internal resistance increase, and power fade. Operating conditions, such as temperature, charge/discharge rates, and depth of discharge (DOD), significantly impact the rate of battery degradation. High temperatures, high charge/discharge rates, and deep cycling accelerate degradation, while moderate temperatures and shallow cycling can extend battery life. Historical usage patterns, including the number of charge/discharge cycles, the average DOD, and the operating temperature range, provide valuable information about the battery's degradation history. By analyzing the current SOH, operating conditions, and historical usage patterns, it is possible to estimate the RUL of the battery using various modeling techniques, such as electrochemical models, statistical models, and machine learning algorithms. These models can predict how the battery will degrade in the future and estimate the time until it reaches its end-of-life (EOL) criteria, typically defined as when its capacity drops below 80% of its original capacity.