App Store app in iOS 11 by default will play video preview of apps to give you better idea about the apps. This autoplay feature is helpful but puts strain on your battery life and uses up data bandwidth. To disable the autoplay, go to Settings > iTunes & App Store.
Tap on the “Video Autoplay” section, and select “Off” to turn it off. Select “Wi-Fi Only” if you want the auto previews but limit them only when connected to Wi-Fi.