I read this from apknite :"My main issue with leaving it overnight is my Quest appears to switch itself back on when the battery becomes fully charged. So it sits there, green charged light on, all the white lights on, humming and heating away - and it doesn't go into stand-by because it's plugged into the mains."
I haven't experienced that. The only times my Quest has turned itself on was when there was a headset update (the Quest was not on charge, and in standby mode). Then, it does stay on and drain the battery.