How can I find if I have a rogue background process killing cpu and battery? On my Android phone (Sony Xperia Z3 Compact), I have a situation where it sometimes goes very sluggish, and the battery drains quickly.

This seems to happen after roughly once a day, and lasts until I restart the phone.

I haven't been able to get any useful info out of the battery info in settings, although the %s there sum to quite a bit less than 100%, so I'm concerned there is some dodgy system process killing my phone.

Is there any way I can get a list of all processes and current cpu usage? I've had a look in the play store but not found any apps that can do this.
Enable Developer Options on your phone (usually done by tapping the Build Number in Settings &rarr; About phone 7 times) and look for an option named "Running Services" in it. It shows a list of all applications which are running, for how long, and the amount of RAM they are using. If you tap on the app it will also list those services of the app which are running and allows you to force stop each service.