Battery drains

1997 NISSAN HARDBODY
110,000 MILES • 2.4L • 4 CYL • 2WD • AUTOMATIC
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G. FROSS
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Truck has a new battery, but when it sets a couple of days the battery goes down. Testing with a meter shows absolutely no drainage, but the battery still goes down. Any ideas?
Nov 26, 2017 at 12:31 PM
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CARADIODOC
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How are you testing for a drain on the battery?
Nov 26, 2017 at 1:55 PM
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G. FROSS
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I believe I found the problem. Thanks for your time.
Nov 27, 2017 at 8:10 AM
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CARADIODOC
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That does not help anyone. What did you find and how did you find it? We like to add your information to our memory banks so we can help others.
Nov 27, 2017 at 2:53 PM
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G. FROSS
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I disconnected the ground cable, and jumped a DC amp meter between the cable and the post, and pulled fuses until I found the right one.
Nov 27, 2017 at 7:31 PM
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CARADIODOC
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Nice. Be aware that starting in the mid 1990's, a lot of cars had computers that needed up to twenty minutes to go to "sleep mode". Until that occurred, they could draw up to three amps. The problem comes when using a digital amp meter and you want to switch ranges. You need the 10-amp scale to avoid blowing the internal 2-amp fuse, then when current drops, you have to switch to a lower scale for more accuracy, and usually you have to move the positive probe to a common jack. Removing the lead from the meter's jack opens the circuit, that wakes up the computer, and that blows the meter's fuse. Darn the bad luck.

Also, all meters use a "break-before-make" switch to change the ranges. Turning it also opens the circuit for an instant before it connects to the range you are moving it to, and that will wake up the computer.

Unless the manufacturer specifies differently, the maximum acceptable current draw with the ignition off and computers asleep is 35 milliamps, (.035 amps). At that rate, Chrysler says a good battery will be able to crank the engine fast enough to start after siting for three weeks. Cadillac is one notable exception that allows up to 50 milliamps.
Nov 27, 2017 at 8:13 PM