I think many android users know about the force stop app trick. You can use shelter to set an app to autofreeze so it is active only when you are using it, and you don't have to worry about forgetting to force stop. It also allows you to run another copy of whatsapp or whatever app.
Shelter is free and open source.
https://play.google.com/store/apps/details?id=net.typeblog.shelter
https://github.com/PeterCxy/Shelter