Energy consumption due to network traffic on mobile devices continues to be a significant concern. We examine a range of excessive energy consumption problems caused by background network traffic through a two-year user study, and also validate these findings through in-lab testing of the most recent versions of major mobile apps. We discover a new energy consumption problem where foreground network traffic persists after switching from the foreground to the background, leading to unnecessary energy and data drain. Furthermore, while we find some apps have taken steps to improve the energy impact of periodic background traffic, energy consumption differences of up to an order of magnitude exist between apps with near-identical functionality. Finally, by examining how apps are used in the wild, we find that some apps continue to generate unneeded traffic for days when the app is not being used, and in some cases this wasted traffic is responsible for a majority of the app's network energy overhead. We propose that these persistent, widespread and varied sources of excessive energy consumption in popular apps should be addressed through new app management tools that tailor network activity to user interaction patterns.