Alleviating the low-battery experience of mobile users through heterogeneous batteries and their scheduling

Abstract

Mobile devices like smartphones have become deeply ingrained in our lives and are now truly essential. Therefore, mobile users experience a lot of stress when the battery of their devices is low. Notably, it is reported that mobile users suffer symptoms such as low battery anxiety and nomophobia (no mobile phone phobia) when they experience low battery. Despite the physical advance of an existing single-cell battery system, mobile users are still suffering from low battery anxiety and nomophobia. With a careful analysis of users’ battery usage behavior collected for 19,855 hours, we propose a heterogeneous battery system, MixMax, consisting of three complementary battery types tailored to minimizing the low battery time. While composing a heterogeneous battery system opens up a chance to simultaneously improve the capacity and the charging speed, one must face non-trivial challenges to determine the ratio of enclosed batteries and charge/discharge policies during the run-time. They are not only difficult to design due to the complex behavior of mixing batteries, but also, there are almost infinite candidates for the choice to design them. MixMax gracefully unwinds the complexities as it formulates the decision-making problem into an optimization problem and decomposes it into multiple sub-problems instead. To evaluate MixMax, we fabricate coin-cell batteries and experiment with them to model an accurate battery emulator which sophisticatedly reproduces the dynamics of battery systems. Our experimental results demonstrate that MixMax can reduce the low battery time by $24.6%$ without compromising capacity, volume, weight, and more importantly, users’ battery usage behavior. Additionally, by classifying users based on their battery usage patterns and providing a customized MixMax to each user cluster, the customized MixMax is able to reduce battery shortage time by up to $36.1%$. Lastly, we prototype MixMax on a smartphone, presenting the practicality of MixMax on mobile systems.