My iPad Pro 10.5" has been experiencing ~10% drain each day as well, just like your situation (I have wifi turned on and connected to my home network though). Genius Bar ran diagnostics which came back with a complete clean bill of health--guess that's both a good and a bad thing for my iPad). Currently I'm running another battery drain test/check but this time I wiped my iPad and set it up as new, did not restore my backup to it, put it in Airplane Mode, disabled background refresh and notifications (the latter should in theory prevent any home/lock screen activity), and did not sign into iCloud and iTunes (thus giving my iPad no reason to even try to talk to iCloud or iTunes); I will check on battery usage at the end of the week to see what the numbers look like.