IP 6S has had battery replaced by AppleCare.
- it's connected to Apple Watch 1
- wifi will be on, but not active (i don't turn it off) except to say that I think it sniffs out BT hotspots and connects briefly as i pass.. there is wifi from a 3 MiFi in the car (for customers) which is on but phone is excluded from it
- no, phone not charging. well, not often!
i do notice that when I am at home and sat with plantronics m55 ear piece connected, every so often though only half a metre away, the headset reports phone not connected. I haven't noticed if this is a regular interval. I've seen plantronics issues mentioned elsewhere and have asked PLantronics, they aren't aware of an issue with Apple products (though they did tell me to download their hub software and make sure headset firmware up to date)
In the car usually I don't know it isn't going to work until i try to answer a call (then can only hear caller by risking licence to put phone on speaker). poor... sometimes, e.g. if i ask Siri something, car takes over then Siri can't hear me, and thee whole thing then gets in a complete knot (and i can't even drop the "call"). very occasionally i do get a message saying phone unavailable (from car). again, very occasionally after working! the car seems to reboot and remake the connection (which subsequently from experience won't work).
so, long answer short - no i don't think that my issues correspond with yours. regrettably it's not that easy :-(