2002 Ford Focus sits over night and battery goes dead?

In this case first thing to be checked is car alternator and battery.
Load test the battery and see if its checking ok,Bench test the battery and alternator and confirm both are good.

Also see if any lights inside or outside the car is not turning off after you turn the key off.
If any light is remaining ON,that there is your problem.

But if all things checks out ok,then its issue with radio.

As long as the alternator is charging ok (14.0 volts) and the battery load test passes is the radio on the 2002.
Try pulling the #31 radio fuse and see if the draw goes away.
If it goes away,then yes problem is with car radio.The radio has to be replaced,before that without forget,inspect the car radio wiring.If all wires are checked intact,then radio has to be replaced,its draining your car battery.This problem is very much noticed on 2000 to 2003 ford focus car models and issue is with car radio,causing this.

So without forget,first confirm the other possibilities,if all checked out ok,then yes its issue with car rtadio causing this problem.

This will help.

Thanks.

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