As mobile apps grow in size and technical complexity, the effort of managing the level of strain on mobile phone resources becomes an even greater engineering challenge – particularly given the limited level of os-level access apps have on mobile phones. In this presentation we’ll share insights into our process for reducing battery consumption by the Facebook family of applications on both Android and iOS including: the main causes of battery drain (everything from radio wake-ups to invisible animations), instrumenting and modeling battery drain (without relying on the OS reported battery level), and general best practices for reducing battery consumption by an app.