Yes, the Sprint repair store reflashed with nougat. I would have preferred going back to MM but they could not do that. I did the factory reset just once since it is somewhat time consuming to restore the apps and settings.
The battery is not removable. Safe mode (and "max" power saving mode) turn off most apps, but the power drain is still high. Doesn't seem to be the apps causing it. It started doing this with nougat. Under marshmallow I used at most 10% in 10 hours (I set the phone on my desk and do nothing with it all day). Under nougat, this morning, it used 10% in 4 hours.
The only fix I found was airplane mode, although I am testing that again now since I have not tested that for at least a month.
I realize there should be other complaints, but there are many phone models and the OS will run differently on each of them. That's why I posted under Samsung Galaxy S6. But you are right that there should be more complaints even in this forum. Another possibility is that I had bug in MM that caused my phone to use too little power. Almost everybody I talk to uses a lot more battery during the day although they also use their phones more.
I tested safe mode for a day about a month ago. I'll test that again after I finish my current airplane mode test.
results: safe mode used up 4% in 2 hours consisting of 2% Device idle and 2% Android System. The phone is cold however, so perhaps there is a battery calibration problem? I think I should let the battery run down to zero (or as close as it gets), then recharge.
Let the battery go down to zero until the phone shut off, then turned it back on until it would no longer turn back on. Then charged to 100% with the phone turned off. No change in battery performance, possibly worse. I'm not sure how it calculates the drain for each app. Has my battery gone bad? Why would that happen precisely when I upgraded to Nougat? Would a bad battery show up as high use in Device idle and Android System? Those are always the two highest usages by far.
After updating my s6 to nougat a few months ago and installing the patch, factory reset, partition wipe etc etc tried turning everything off, safe mode i have battery drain of a massive 20% per hour!! Yet my battery usage monitor never shows that amount. Always device idle ir android os highest usage
That is strange, your case is much worse than mine. At least mine is just 2-3% per hour. But your symptoms sound similar: Device idle and Android System are my highest battery uses listed. When I don't use the phone at all, then those are the only two battery uses listed.
When I ran with GSAM battery monitor, it implied that the phone almost never went into deep sleep (it says deep sleep 1% of the time). I suspect your phone is never going into any kind of sleep, it is just staying full CPU usage even when you do nothing with it.