Battery interfaces provide important feedback about how much time users can continue using their mobile devices. Based on this information, they may develop mental models of the types of activities, tasks, and applications they can use before needing to recharge. Many of today's battery interfaces tend to report energy in coarse granularities or are highly inaccurate. As a result, users may find it difficult to depend on the estimates given. We conducted a survey with 104 participants to understand how users interact with various mobile battery interfaces. Based on the survey results, we designed and prototyped a task-centered battery interface on a mobile device that shows more accurate information about how long individual and combinations of tasks with several applications can be performed. Our pilot study of eight users demonstrated that fine-grained information separated by tasks can help users be more effective with and increase their understanding of their device's battery usage.