> If there are two os then the battery would drain very badly, right?

I don't think this is a viable argument because we have no baselines here. In case phones have been running a shadow OS for many years now across the board there just are no phones around to compare battery usages in a meaningful way. "Drain very badly" isn't a figure I can measure when all phones do the same. All the older phones that run through my hands have generally a "bad" battery life cycle; I ascribe that to battery degradation plus technological advancements that have raised the bar.

Not if the dark OS is only activated when a special message is sent to the baseband processor.

So let's expand on this theory: all battery metrics are calculated and faked. This second OS is so lightweight that it does not even affect battery life. It's a conspiracy theory, so it's assumed to be alien technology, the most secret one ever.

This second OS performs very few operations, such as recording and sending data to the network over time when it's connected to the internet. Or it doesn't even need an internet connection. It sends the information every six months, so you don't even feel it. The data is collected in a very lightweight, encrypted, zipped, alien technology way, so it's inconspicuous.