Plus 2) would require additional design, engineering and QA work to implement the code to drain users' batteries. And it would cause plenty of users to uninstal

Plus 2) would require additional design, engineering and QA work to implement the code to drain users' batteries. And it would cause plenty of users to uninstall/complain if Messenger was draining huge amounts of battery. It really doesn't make sense considering Messenger has 1.3 billion users, and remaining battery percent would likely be a bell curve across all users regardless of sample size.