JuiceDefender is a mobile application designed to optimize and extend battery life on Android devices. It offers a variety of features that help users get the most out of their device's battery life, including power saving mode, whitelist/blacklist applications, battery monitoring, and automatic task scheduling. It also provides a "Smart Saving" algorithm that learns user behavior and automatically adjusts power usage settings to maximize battery life. Additionally, JuiceDefender provides detailed battery statistics such as temperature, remaining capacity, battery health, and estimated time remaining. The application also offers a widget for easy access to power-saving functions.
Juicedefender (back in Lollipop, no more since Marshmallow) accurately per app enabled wifi disabled as a preference and data as secondary when an app was launched. And it disabled the connection when the app was closed or the phone was locked. For years this was true. It is the per app control that was the saving for me. I only need the network when I launch a network app.