Re: Not starting, battery drains overnight.
As stated, have the dealer check for the voltage draw and it's location. A healthy battery, alternator and starter are all good, but new, modern cars have a constant draw on them, due to Modules and Control Units, that need to "stay alive", retaining programed information.
As JamesR said, if one of these units fails, or develops a "draw", it can drain a battery just by sitting, in a short period of time.
Determining WHICH circuit is causing the draw is much harder these days with as many as 10-20 onboard computers on one car.