Sudden discharge of battery

2002 VW GTI 1.8L

My battery died not too long ago so I replaced it. A few days later, car wouldn’t start again. Busted out my DMM and found my alternator was on its way out. I now have a new alternator that correctly puts out 14V and a new battery that will hold 12V for a long period of time if disconnected from the system. However, if i leave it connected overnight or over a period of about 5 hours with the car off, I come back to find the battery dead (7-9V or so). Every time i jump it, it starts up right away first try without any excessive cranking or time needed to charge. I’ve checked for a short on random occasions but it always only reads 30mA, which is definitely normal. Also, all my fuses are fine. This problem is driving me crazy. Any ideas out there?

Please describe completely the procedure that you are using to read the current drain. A five hour discharge would imply up to a 10 Amp drain. Of course, that would be with a good battery, which you no longer have. (Car batteries are damaged anytime they are discharged below 10 volts.)

Something is apparently turning on while the car is parked. The current draw you measured is normal alright so the trouble must be occuring later on.

Why do so many people think that all electrical problems are “shorts”? Anyway what you were doing when you measured 30ma was checking for a parasitic draw not a short. Measure again. I also don’t like you saying that your new battery “will hold 12v” it should be closer to 12.6v. How did your DMM tell you your alternator was on its way out?

Sure. I remove a terminal (both give the same reading) and put the DMM in series. it reads 30mA give or take 1 or 2mA every time. If i were to check the voltage across the battery after about 4 hours and by chance my car was not dead yet, it will still read 12.2V or so. No discharge. if i disconnect it, doesnt matter how long i leave the car alone, i will come back to a perfectly fine battery.

Okay, why not try a little experiment. Get an in-line fuse holder at one of the auto stores. Get a 1/4 Amp fuse (less if you can find it) that fits it. Now temporarily install the fuse and fuse holder between either terminal of the battery and the wire that would be attached to that terminal. Wait long enough that the battery should be discharged, and check and see if the fuse has blown. (Doesn’t count if you opened a door or something.) This will test to see if some big load somehow switched on while the car was off.