Within the last few months my 08 Focus has had a drained battery. The first time this happened the alternator was checked and battery was replaced. The alternator was functioning 100%. A month or so later I went out to start my car after not using it for a day, and again a dead battery. Now this morning, after a day of not running, my battery was completely drained. I did notice this time I could hear the sound of something "running" on the inside of my car. Like something keeps going once my vehicle is off that is causing my battery to drain. I know in my 00 E350 van, the auto locks will sometimes lock and unlock until the battery drains. I don't believe this is the case with my Focus. Also, my dash lights are gone but my check engine light and my low tire pressure light remain on. I've had the fuses checked and they seem to be intact. Any idea what is going on?

 

There is a good possibility one of the modules is failing to go into "sleep mode".
If this is the case it will surely drain the battery in a short time especially if it keeps a motor running.
This usually requires a good scan tool to check the modules. Something from outside the vehicle may be preventing the vehicle module from going into sleep mode.
Battery saver feature may also be a consideration.