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Have an intermittent parasitic battery drain.

(2006 Nissan Maxima)
in Phoenix, AZ on January 07, 2014
Can drive car an let sit for a week with no problem. Other times will drive it to work an will have a dead battery by end of shift. Sometimes will die over night on occasions. Have verified that battery is good by letting sit unattached for a week with no loss of voltage. 8 months old battery.replaced alternator also.
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Popular Answer
of Greg's Orange Auto on January 08, 2014
of Gillespie's Auto Service on January 08, 2014
One of the big problems with a parasitic drain like this is the battery gets discharged and left in a constant state of discharge. It takes 48-72 hours with a ten amp battery charger to fully charge a battery once it has been depleted to the point that it could not start the engine. It takes eight hours in a shop with the professional models, and its completely unpredictable how long you would have to drive the car if you jumped it, but in most cases it never gets charged back up by just driving it.

To find what is killing the battery one of the best routines is to first measure the parasitic drain and that is done with a low amps current probe and voltmeter (scope). Then the tech will go to the fuse block and measure the voltage drops across the fuses. Any fuse that has power flowing through it, no matter how small will have a voltage drop occurring across it. This is where a cheap meter won't do, the meter has to be accurate down into the ten microvolt range, that's .0000X V or .0X mV. Once the circuit is identified, then the low amps probe can be moved further down the circuit until the fault is identified. You need a tech who can (and will) work through this problem for you.
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