You've got some problem with your SD card (assuming you have one in there); the media subsystem is Android's internal indexing mechanism for media files, and it will do this if your SD card is corrupt or otherwise has issues (e.g. bad or corrupt media files, etc)
It will normally eat a fair bit of power on a new setup for an hour or two while it does its thing with a full SD card but then it should stop. That's where your problem lies.
I'm on a BBB100-1 and here are my "test" results from yesterday.
This phone is a beast. I missed the Passport battery when I switched to the Priv but not anymore.
Screen brightness was on the lowest setting (adaptive brightness on).
Location was on intermittently.
WiFi on the whole time.
I made two phone calls, both no more than a couple of minutes long.
Phone came off the charger around 3am and kept chugging until 10:30pm with I'd say, medium to heavy use for me. Workhorse.
The phone's estimate of how much battery life was left was spot on. Both times at 50% and 25% remaining, it accurately predicted how long I had left before I had to reach for the charger.
I kept my Priv fully charged all the time at the office. I would pull the cable off once the battery hit 100% and plug it back in every few hours. That way, I'd always have a full battery if I had to run out to a meeting. I will not be doing that with this phone.
you have some crap app that's killing your battery. I have only had my CDMA since last Thursday but after the first day setting up all the software battery has been stellar
Mine as well. I am very impressed with mine. I use full screen brightness on mine so the battery life isn't 2 days but better than my Pixel, iPhone 7 plus and S8 plus.