Why is my brand new battery constantly being drained?
My battery died, so I replaced it with a brand new one. That one died as well, so I replaced the alternator with a brand new one, again, the battery died. What could be the problem?
I know you said that you replaced the alternator but I'm not sure if the vehicle has a separate voltage regulator or whether it is inbuilt into the alternator so check the charging voltage across the battery with the engine running is in the range 13.8VDC -14.5VDC If it is less than 13.8VDC the battery will not charge and will discharge slowly as it will be helping the alternator to run the electrics in the vehicle.
Be SAFETY AWARE when you test as the engine is running!
How long does it take to go flat?
Have you checked that everything that can be turned off has been, e.g if the boot (trunk?) courtesy lamp is left in the Always On position it can drain the battery after a day or so. Also if there is any after market equipment that has not been wired via the ignition key power supply feeds but powered directly from the battery
Otherwise, with the engine switched OFF you may have to remove the -ve cable from the battery and place an Ammeter (function found in a DMM - digital multimeter) in series between the -ve post of the battery and the -ve battery cable and read the current flow. There should be a reading of about 100mA or thereabouts as there is always such things as an immobilser and alarm system (if fitted) and some other electronics that need to be kept powered.
If you read a lot more than this then you'll have to start pulling fuses one by one and watch the Ammeter until the current falls to a more acceptable level.
Once you find the fuse you'll know what circuits are being supplied and hopefully what may be happening.
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