I have the same problem with my battery at my Oneplus One as a lot of users with other phones.
With WIFI and without network there is no problem.
NOT using my phone it is empty within about 10 hours
I bought a OPO and installed UT yesterday with snap on Ubuntu 16.04. after I have UPDATED the system!
I selected the device manually.
I had to disconnect the OPO from the PC to get it into the recovery mode and than connected it again.
Than the installation began automatically.
Just sitting down and waiting for a while (about 10 minutes).
Everything is working perfect
So it is worth to buy a OnePlusOne !!!