I don't really like Clean Master or any other of this fake â€œTask killersâ€, because I think they include to many ads, so that it is more like adware than a helpful tool. And most of the tools also don't really work well.
But to save battery, it's a common method to kill running app tasks.
For this feature I use the app â€œGreenifyâ€. It will kill all the running apps for you.
To work, the app uses the â€œAccessibility servicesâ€, an API in the Android system, that allows the app to perform click events.
Using this feature it can do all the app killing. If you regularly do this, you can use your phone much longer, before recharging. This also improves your battery life.
In addition to this, the app is also ad-free, which is an outstanding feature compared to many other task killers.
If you want, you can also buy a premium version, which unlocks some more features for rooted phones and phones where the XPosed framework is installed.
You can download the app on Google Play.