There is a draw on the battery, make sure all of the auxiliary lights are off ie dome lights, trunk lights visor lights glove box lights, if all light are off then to check it you need to disconnect the negative battery cable and put a test light between the cable and battery post if the light turns on you have a draw that will kill a battery overnight, the next thing you need to do is disconnect the alternator even though it is new it may not be good, if the test light goes out then you have found your problem, if it is still lit then you need to start removing fuses one at a time until the light goes out, make you note the placement of each fuse as you go, when you do find the circuit that turns off the light then you have to find out what component is causing the draw.
Once again T. S. Has given you and others with this problem a clear and easy way to check for battery drain problems.
Change out ignition switch.
After 3 batteries (everyone said the alternator was fine) and 3 weeks in an auto electric shop my backyard mechanic found the problem with a short in the original radio. New radio for over 3 months now and not a dead battery yet.
Thats why you run battery draw tests, but it shouldn't have taken three weeks to find it.
I did the battery draw test myself before I ever took it to anyone and I personally watch two others do the draw test. The draw test did not pick up the battery drain. Just by chance I was having the old radio removed to make room for a new one and it was over a weekend and to everyone's surprise the car started right up.
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