Battery SoH Estimation Using Charge Time and SoC Interval
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Solution Overview
Problem
It is challenging to accurately determine the state of health of rechargeable batteries in wearable devices, especially those that have been stored for a long time or refurbished with unknown quality, as existing methods are unreliable and often require additional costly hardware.
Innovation Solution
A wearable device with a battery gauge system that provides a state of charge metric, which determines the state of health based on the charge time interval by comparing it to a reference time interval for a new battery, using a known relationship between the charge time and the state of charge increase, without requiring additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional hardware is used to determine battery state of health, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The battery gauge system that already exists in the device to track state of charge is repurposed to also determine state of health. The same hardware components (current sensor, voltage monitor, microcontroller) that track charge level are used to measure charge time intervals and calculate SOH, eliminating the need for separate diagnostic hardware.
Solution Approach 2:
The battery gauge system is made multi-functional by enabling it to perform both state of charge monitoring and state of health determination. The charge time measurement capability is leveraged for dual purposes: managing battery charging operations and assessing battery degradation, thereby avoiding additional hardware requirements.
2Device complexity
If charge time interval measurement is used to determine state of health, then device complexity is reduced, but measurement precision may be affected by charging conditions
Solution Approach 1:
The method measures charge time interval for a specific state of charge change (e.g., 10% or 20% charge increase) rather than absolute charge levels. By standardizing the measurement to a fixed charge interval and comparing it against reference values from new batteries, the system compensates for variations in charging conditions and achieves accurate SOH determination without complex hardware.
Solution Approach 2:
The system continuously monitors the relationship between charge time interval and state of charge metric, using this feedback to update the state of health determination. By comparing actual charge times against expected times for a healthy battery, the system can detect degradation trends and adjust measurements accordingly, improving precision over time.
Data Source
AI summary
A computer-implemented method for improved determination of state of health (SoH) of a battery of a device can include determining that the device is in a charging state such that a charge of the battery is increased over a charge procedure; determining that a state of charge (SoC) metric of the battery reported by a battery gauge system has increased by a fixed SoC interval; determining a charge time interval over which the SoC metric of the battery has increased by the fixed SoC interval; and determining a SoH metric indicative of the SoH of the battery based at least in part on the charge time interval; wherein determining the SoH metric is based at least in part on a known relationship between a reference time interval representative of time required to increase a reference battery at full SoH by the fixed SoC interval and the charge time interval.