No one is going to be able to tell you that unless the app is advertising itself or someone has seen the exact same popup ad. More than likely it's an app (or malware) that seeks to generate ad revenue.. the upshot of which is that what you see in the ad may have nothing to do with the app. Google image search does not appear to have a match to it.
Still if you have any battery or power apps installed, they would have to be at the top of your suspect list.
Rather than make us try to guess, post a list of all your third party apps that you have installed and we may be able to spot the culprit in that list. Or in the alternative, install an ad blocker program on your handset.