Bad alternator or corroded or loose cables.
If the engine is running, then no. The alternator constantly keeps the battery charged.
If the battery, drive belt and wiring are okay then I would suspect the alternator is faulty. Your local auto parts store can test the charging system for you at no cost.
Your car lost power while you were driving and it will not start now because the battery is depleted.
Not likely.
Yes the car radio will drain the life out of a battery. The way it works is the battery acts like a plug-in that is in your house, and everything is hooked to it so after a while of using it all the power is draned from the batery and it is dead.
The Legacy subwoofer will really drain your battery. It's not a good idea to run it while you're not running the engine.
A car battery in any car would drain due to a short in the electrical system.
While the car is running the alternator should be recharging the battery faster than stereo can drain it. I suspect you either have a problem with the alternator or its time to get your battery replaced. Until you get it fixed, if you don't turn on the radio, it wont drain your battery :) If it is a high power model, it needs to be wired directly to the battery.
The car will stop if the battery cable comes loose.
If the ashtray light is not working it will not drain the battery.
You can get a car alarm that uses it's own battery so wont drain the car.
Eventually, yes, it will.