A short in the wiring.
Bad Battery. Bad Alternator. Lights left on by mistake. Something left running. Exc.
Yes, a loose battery cable will prevent the alternator from charging the battery. The drain on the battery is not caused by the engine not running unless an accessory is left on. Most likely, the drain is caused by accessories (radio, lights, etc) while the engine is running due to the battery not receiving its charge from the alternator and then not having enough charge left to start the engine.
A raidator in need of a flush will not cause a battery drain.
Have you had the alternator tested? Often a bad internal diode can drain the alternator overnight.
If the alternator is installed incorrectly, yes, it can drain the battery.
Shorted diodes in the alternator.
Yes. If the alternator is dead and you drive the vehicle, all the power is coming from the battery and it will eventually drain completely. Also, if a diode is shorted inside the alternator, that can drain a battery.
Your alternator could be bad.
dead cell in the battery or something is on pulling power from the battery.
It doesn't actually drain the battery, but without a working alternator to recharge the battery it will only discharge as the car is operated.
Bad alternator and/or belt. Your battery isn't being re-charged while you run the engine, so the electrical things drain the reserve from the battery.
Yes, a dead cell in the battery or something is on drawing power from the battery.