I have a 2004 Chevy TrailBlazer that recently refused to start for my wife. I’ve got it going again and with a new battery. but I checked the key-off battery current drain with an ammeter (negative lead disconnected, meter between the cable and the battery) and the drain is 92 milliamperes. That s…

This is Dave again. If that link mentioned above does not work, try going to Google and typing in: “Parasitic Current Drain”. That should bring it up.

To me, 92 doesn’t sound that high—that’s less than 1/10 of an amp, or about 1.1 Watts of power. If the car has keyless entry, a stereo, Onstar, an alarm, in addition to the vehicle’s own computers, it’s possible that just maintaining the memory of these devices is using this much power. Of course …

92 milliamps sounds high. I think it should be around 50 milliamps. Did you wait about 30 minutes before checking the amp draw? When the battery is disconnected then reconnected it takes about 30 minutes for everything to power up then shut down. So if you didn’t wait long enough you could be getti…

Just opening the door can wake up some microprocessors in some vehicles. That puts you in the awkward position of having to crawl in the window to pull fuses after you wait for everything to go asleep. 90-100 mA seems a bit high, but look at it this way. I presume that your TB has a pretty big ba…

Dear Willey, Yes, I checked the current over a period of several hours and then again after sitting all night. Thanks.

Dear Beadsandbeads - Your reserve calulation is interesting. I expect the battery gradually lost ground after many weeks because my wife usually makes short trips with the car. On her last trip, as I mentioned, it just couldn’t crank the engine again. That fits with your reserve calculation at le…

Regarding accuracy of ammeter – I just checked it with known resistive load and it checks out just about perfectly. Three 470 ohm resistors in parallel make 156.7 ohms. Battery voltage of 13.55 should give 86.5 milliamps. And that’s what it reads. - Dave

Here is a TSB that might apply: Bulletin No.: 02-01-39-007B Date: November 05, 2007 INFORMATION Subject: Automatic Dual Zone HVAC Battery Draw Models: 2004-2007 Buick Rainier 2003-2008 Cadillac Escalade Models 2002-2008 Chevrolet TrailBlazer 2003-2008 Chevrolet Avalanche, Silverado, Suburb…

Before anyone can tell you if 92ma is normal, you need to provide more information about your particular Trailblazer. Is it 4x4? Is it equipped with OnStar? Do you have any aftermarket accessories? I own an '04 LS 4x4. I can check my normal draw as a comparison but I want to know if we’ll be compar…

What is normal parasitic current drain?

Maintenance/Repairs

daveinbellingham October 6, 2008, 11:46pm 6

Thanks for the reply. The meter I used was a pretty nice one – a digital multimeter with three current ranges available. I have a DC Clamp ammeter ordered so I can check things with the cables connected normally. That will be about 5 days from now, though.

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What is normal parasitic current drain?

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