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Discussion Starter · #1 ·
Hey VMF,
Ever since I replaced my alternator, and voltage regulator, for some reason or another, my battery keeps draining itself. I took the brand new (but drained battery) to autozone and got it charged, then I put it in the car, moved it like about 1 block and parked it. I left it today and went in another car to school, then when I come back tonight to try to jump in the car for a quick errand, the battery is basically drained. I have no idea how I should go about trying to diagnose this. What could be draining the battery? The car has absolutely nothing that was on, it was just sitting. If anyone has any ideas on what there could be, or where I could even start with to figure out this problem? Thanks
 

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VMF Full-Timer
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You want to take this one Midlife?
 

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Be sure your battery is fully charged. I know that sounds basic but a partially charged battery can cause that problem also. If you have a basic test light that uses a small bulb,you can test for current draw when key is off. Disconnect one of the battery cables and put the test light in between ( series circuit )the battery terminal and the disconnected cable. The light should not light up. Be sure everything is off and doors are closed,etc. If there is a current draw the light will light from that current flowing. Take one fuse at a time out to see if the light goes out. If that does not get you a cause, disconnect the battery connection at the alternator. Then the regulator. One at a time will find the culprit! Aftermarket radios not connected correctly or other loads that can draw without the key on are suspect also. Just go slow and methodically,you will get it!
 

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Here's my method...

Disconnect the negative cable on the battery, and use a digital volt-ohm meter that can read 10 or 20 amps DC. Put the amp-meter between the battery post and the disconnected battery cable. You'll see what the current draw is. Now, how to find the offending item?

Start by removing the amp-meter (use it just by touching the terminals...don't hook it up semi-permanently), and then remove the fuses one by one. After each fuse, test the current draw. If the problem is controlled by a fuse, then whatever fuse lowers the current to less than 100 milliamps contains the problem. If none of the fused circuits are at fault, disconnect the voltage regulator terminal. Test the current draw. If that doesn't do it, remove all lines from the starter solenoid positive battery side except the alternator and the battery. Test the current draw. If still high current, remove the wire to the alternator. If that doesn't do it, then the starter solenoid is bad.

This is just a problem of eliminating circuits until you find the one that has the current draw.
 

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The fun of electrical shorts .
 

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You said you changed the alternator. That could very well be your problem. I had a diode go out in the alternator in the Shelby once and it would drain the battery overnight.
 

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Discussion Starter · #7 ·
Is there some way I can test this alternator diode idea? I would just have to turn over the engine and check if the batterys amperage is fluctuating correct? I'm going to spend this Sunday troubleshooting, I want to try to test all routes!
 

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Hello,
I had a similar problem, and it turned out to be a bad cell in the battery. My home battery charger was showing a bad cell code, and the parts store confirmed a partially bad cell. It was one of the new autolite batteries.
Hope this helps,
Joe
 
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