Before I had any Apple product, my computer was Windows and my tablet and smartphone were Android, I used this Buienalarm. (We had a flood in our cellar in 2011, at that time I installed that Buienalarm)
This is one of the only apps I still use today I've always used as long as I own Apple products. It even was one of the first apps since I started using smartphones at all.
So about my battery: it was fully charged after DFU reinstall. With charger disconnected, I set-up iCloud, Touch-id and Wifi settings. I immediately went to app store do download that Buienalarm. Opened it, set-up, had the shower map visible and closed it down by pressing the home button. Still 100%. At that time I did something else, came back and the battery was 94%.
Checked the battery stats and it showed me a huge background drain just of that app. Nothing else was installed.
Then, I reported this issue here. While typing my previous post, I've got another idea...
To be certain if iCloud doesn't do anything wrong (due remaining settings or something), I created a brand new iCloud emailadress, with a brand new iCloud. I installed all that on that iPad. After that one app: Buienalarm. Again, after one hour in the battery stats: 25 + 32 min background activity. 4% battery drain during this time.