Environment-aware estimation of battery state-of-charge for mobile devices

Abstract

Reliable operation of mobile devices, such as smartphones and tablets, has become essential for a great many users around the globe. Mobile devices, however, have been reported to suffer from frequent, unexpected shutoffs - e.g., shutting off even when their batteries were shown to have up to 60% remaining state-of-charge (SoC) - especially in cold environments. Their main cause is found to be the inability of commodity mobile devices to account for the strong dependency between battery SoC and the environment temperature. To remedy this problem, we design, implement, and evaluate EA-SoC, a real-time Environment-Aware battery SoC estimation service for mobile devices. EA-SoC estimates the battery SoC with a cyber-physical approach, based on (1) a thermal circuit model in the cyber space capturing the physical interactions among the battery discharge current, temperature, and the environment, and (2) an empirically validated data-driven (i.e., cyber) model for the physical relations between battery temperature and battery resistance. We have conducted 35 experimental case-studies with two Nexus 5X smartphones to evaluate EA-SoC. EA-SoC is shown to report an average of 3% SoC when the phones shut off even in a -15°C environment, while that reported by the phones' built-in fuel-gauge chips could be over 90%.