the vehicle needa a new voltage regulater,this should have been checked before battery and alternator as its the cheapest part to replace
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.
Voltage regulator or loose wire.
If you have already checked the connections on the battery I would suggest testing the alternator and the battery. If the battery will not take a charge or the alternator will not give a charge you could have similar problems.
Auto Zone will check your charging system for FREE at most stores. Have them check your alternator.
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.
your alternator charges the battery while the car is running. The alternator actually puts out a higher voltage than 14 volts while it is running, but it is reduced by a voltage regulator (most of which are already built into the alternator housing), to prevent damage and premature death of the vehicles battery. While your car is not running, the alternator is not charging the battery, and the 13.5 volt reading you get is just the measurement of the voltage the battery is holding at that given point.
It sounds like you have a break in the wire which connects your alternator to your battery, get it checked out.
Some new alternators will not charge unless the battery has a full charge already.
It could be the alternator going bad or has already gone bad or the battery could have a bad cell in it keeping it from charging. The battery cable ends may not have good connection for it to charge correctly. The hot wire to the alternator probably needs to be changed because if that wire is bad it too would keep it from charging. Last the plug that plugs in the side of the alternator (round w/ green wire and green and yellow wire) it too would keep it from charging. If it is not none of which I said that you might want to consider in a short in your wiring harness if its a short it will take time to locate it.
Check your battery post to make sure u have a good connection
It's easy to distinguish if your car has a damage alternator or battery. The first thing you do is to start your car using your old battery then, once the engine is running then remove the cable from your battery, if the car still running that means the alternator is still charging but is it enough? so you have to measure the current that is being generated by the alternator using a multi tester. If the reading from the tester can reach 13 to 14 volts then your alternator is still good. If not then the carbon brush of the alternator might need to be replace or the IC. If your car battery is already leaking then it possible that the plates are already damage, or if you have tried to charge your battery but the power is easily drained then it needs to be replace. i hope this can help ......... deep
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.