You have a short - it's hard to be more exact than that, but if you disconnect the battery and charge it outside of the car and it stays charged, you have a short. If it does not stay charged, you need a new battery.
Voltage regulator or loose wire.
It means something is wrong with your charging system. Can be a loose of corroded battery cable, defective alternator or a battery with a dead short.
It sounds like you have a break in the wire which connects your alternator to your battery, get it checked out.
the vehicle needa a new voltage regulater,this should have been checked before battery and alternator as its the cheapest part to replace
Some new alternators will not charge unless the battery has a full charge already.
Check your battery post to make sure u have a good connection
go to a auto parts store like advance auto and have them check your computer to see why it is on. they do this for free. this might give you a idea on why its on. if you havent already.
If you have replaced all this it may not be a belt. It may be your alternator itself. These have bearings inside them and they do wear out. The only way to check is to remove the belt and spin the alternator to see if that is what is noisy. It may wobble if the bearings are bad. It should turn smoothly if not.
try playing with the battery cable connector. mine had a bad connection and it wouldn't turn over every once in a while. you might need new connectors
Serpentine belt? You may have to remove to tighten alternator
Blown fuse or wiring defect for the bulb you have already replaced. You have replaced the wrong bulb. The new bulb was defective.
Disconnect the cable from the alternator and see if that stops the draw. If it does, the alternator may be defective. Otherwise there may be something else drawing current.