Doesn’t a modern smartphone have something like a 4000 mAH battery? And that lasts most people all day with room to spare? Even 100 mA every few minutes will get noticed, if someone has their phone off and expecting consumption to stay minimal.
And that’s the key thing here, you’re not just building a tracking platform but you are building it into commodity phone hardware without the users consent, and without them noticing. Any phone that burns that much power while off would likely get replaced by the user. Do you think the phone vendors are in on it?