GPS is certainly the device that is draining the power. One of your apps is accessing the GPS system and powering it up, presumably not getting the response it wants, and continuously repeating a request for positional data. Depending on where you are at the time the location is demanded by the app, you may not have a GPS signal available, so no valid data is returned. Perhaps at this stage, the app shuts down, but fails to turn off the GPS module.
Anything to do with social networking, fitness monitoring, mapping, games, or finding a lost, stolen, or misplaced phone could be the culprit. Even something a apparently innocuous as a news feed might be tracking your position to provide you with local news, or advertisments tailored to your location.
Because the positional data is a software request via the core operating system by another program, you will not see the GPS module flagged as being active because the software request has effectively gone behind your back. If everything worked normally, there would be a blip of activity as the request was serviced and the GPS module would power down, and the app requesting the data would be satisfied and just get on with doing its thing. If you are travelling via underground or in a tunnel or other shielded location when the request happens, the software throws a hissy fit and does the equivalent of leaving a phone off the hook on continuous redial.
It is the GPS module that is consuming the power. Now you have the onerous task of identifying which rogue app is causing the issue. I would suggest dumping everything except the stock apps, then reintroducing the ones you really need one at a time until the problem recurs. A right pain, but it is the only way to be sure.
So basically a factory reset, run it for a couple of days to see if the fault recurs, then reinstall the other apps you use one at a time every couple of days until the fault happens again. It is possible that two apps are interacting in a way that provokes the fault. Other people won't necessarily have exactly the same apps or software version numbers, so they never have the problem, even though they appear to have an identical set up.
Last edited by G0ULI; 19th Apr 2017 at 00:20.