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I've recently started having a bit of trouble with my car. I typically drive my car to and from work each day. A couple weeks ago I went on vacation and when I returned, my car battery was as dead as could be. The battery was already a couple years old, so I went to the local auto parts shop, purchased and installed a new battery.

This morning, after it had sat through the weekend, it wouldn't start and was completely dead. I drove the car at lunch, and it started without any trouble. Furthermore, other than the incident a couple weeks ago and this morning, I haven't had any form of trouble starting my car. It's always started quickly, without any trouble.

I checked how many amps the care was pulling while it was off and it was .78 amps. Could this slowly kill my battery after a few days or is that a normal power draw for a car that isn't running?

FYI, My car is a 95 Buick LeSabre. Also, I'm not 100% sure that the lights weren't on a couple weeks ago, however, I am sure that my lights were not left on over the weekend, nor were the internal lamp lights. If something is drawing power, it's something that isn't immediately noticeable.

While a typical car is off, how many amps does it pull from the battery?

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    Do you have a security system that could be triggering something, and waking the car up?
    – FossilizedCarlos
    Jun 19, 2012 at 2:57
  • No, there is nothing like that. I'm thinking it could be a bad relay that's stuck in an open state. However, before I start pulling fuses and testing the amps I thought I'd verify whether .8 amps was high or not.
    – RLH
    Jun 19, 2012 at 12:09
  • what did you use to measure current draw when the ignition was off? 0.78A seems incredibly high.
    – Rory Alsop
    Jun 25, 2012 at 12:36
  • Rory Alsop: I used an Amp/Voltage meter. I work in engineering and I was assisted by an electrical engineer. Or should I really say... I was assisting an electrical engineer who was helping me solve this problem.
    – RLH
    Jun 25, 2012 at 12:43
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    Just fyi, typical drain key off (and the vehicle must sit for 30-45 minutes to ensure all modules go to sleep as well! ) is to be under 0.05 amps, or 50 milliamps.
    – Drake Clarris
    Oct 8, 2013 at 14:54

7 Answers 7

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Not sure what it "should" be pulling, but anywhere near a whole amp is way too much and will drain the battery in no time. Are you sure you tested right? Often the pull when you first connect the battery can be a lot higher than the steady pull since you might be charging some capacitors, etc. If it stays that high you definitely have a problem, possibly a partial short.

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    R..: I disconnected the negative terminal and measured the draw with a meter from the line to the battery. A couple days later, I started pulling fuses and measure the current from the fuse box. I found a line (for the power mirrors/interior lights at my feet) that was pulling about .63 amps. Since I don't need floor lights and my mirrors rarely need to move, I just pulled the fuse until I can take the car into the shop. So far this has helped.
    – RLH
    Jun 25, 2012 at 12:45
  • I don't believe charging of capacitors could occur for more than a second, or else the capacitors would need to be very, very large indeed. Typical capacitor values are at most few millifarads.
    – juhist
    Dec 26, 2015 at 10:46
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0.10 amps will kill your battery quick like, you should get it down as close to 0.00 amps as possible. My experience was that to keep the radio stations, etc. it takes about 0.01 amp on the meter. So yeah, you got something going on... In my case, it was the key lock light staying on and the door lights (or rather door light relays) staying on.

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You want to perform a Parasitic Battery Drain check, as shown here. Once you find the culprit, isolate and correct.

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Mine was pulling 3amps, 3.6 amps to be exact. What had happened was my Volt Regulator, that regulates how many volts run through your car, went bad. I had boosted and jump started my battery over 30 times, I knew it wasn't the alternator because in the 90s they didn't have the regulator in the alternator and if it was the Alternator the car would run dead on the road. This wasn't the case because it charged the battery after start, nor was it the starter because as long as I had power it would always start. Replaced the battery and the next day I had the same issue. So I hooked up the Amp Meter and set it up so I could see it, and began disconnecting and reconnecting a lot of wires. It took over an hour going through all the engine's main wire connectors on one side. Got to the other side, looked at the Volt Regulator, and said 'hmm... it has a connector why not?' took me a few minutes to wrestle it loose but when I looked at the Amp Meter it was no longer reading 3.6 it was reading -0.22 like I had it set to.

The Cause? perhaps age but most likely corrosion. Plugged it back in after cleaning it, the thing started heating up like a stove top and you could smell it cooking. A brief smoking period and I disconnected it again and knew it was done. Replaced it, and I have no draw when my car is Off and no longer have these issues. So if your having this issue as well, and your battery is going dead in a few hours or even one day of sitting. Don't be afraid to figure out where your Volt Regulator is, and find out if that could be the case.

My Car is a 1990 Lincoln Mark VII and I fixed my problem without spending more than 30$. It may be worth it to look into it.

Now this does not discredit Alternators, Starters, and Bad Wires from being a plausible cause or malfunctioning pieces. But it gives you a lead on if this is your issue. Because I couldn't find anything helpful that pointed me this way. So I'm trying to help you the reader by reaching out with my experience.

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I've come across this many times.

The acceptable current draw should be around 0.03Amps. If that can't be achieved upto 0.075-0.1 can be acceptable if the vehicle is driven most days.

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  • Terry Gould said, > The acceptable current draw should be around 0.03Amps. If that can't be achieved > upto 0.75-0.1 can be acceptable if the vehicle is driven everyday. I'm guessing you meant 0.075 - 0.1 amps
    – bill shockley
    Jan 1, 2017 at 14:02
  • ok I'm adding usb port that pulls .017 no load. I should be ok.
    – danny117
    Feb 14, 2018 at 17:43
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Can be a lot of fun to track down electrical parasitic culprits? Had one battery draw that caused soft brake light bulb contacts to re-form into concave shape from convex shape touching brass wiring contacts. Caused from too much bulb heat? Never-ever saw brake lights on while parked with foot off brake either. Weird! Did track down to faulty brake light switch and likely bulb defect. Some electrical problems are complex, not singular. Makes twice as hard to diagnose.

IE: Many brake light switches do not turn off power with ignition. Changed bulbs and switch to repair. No re-occurrence of problem. Shook head twice with that one and was easy to miss at first.

*Could try battery disconnect switch or disconnecting Negative battery cable as temporary easy fix "solution?"

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it sounds more like your charging system is failing. I had exact same problem and it turned out to be my alternator had failed. Some alternators have internal circuitry to charge your battery and sometimes this internal circuitry is external to your alternator. All the AutoZones near me offer free test to determine if alternator is putting out right voltage to be able to charge battery.

It's plausible but rare something could all of a sudden drain the battery. Usually when an electronic part fails it fails by opening the circuit; if it failed and shorted you would have blown a fuse or fusable link.

I would have your charging system inspected.

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    The .78amp draw at rest shows this is nothing to do with charging, but instead shows something is just drawing too much current.
    – Rory Alsop
    Sep 29, 2013 at 11:26
  • I guess I should have clarified this in my answer. You're right Rory but some vehicles take longer to come to rest. Onboard ECUs may run for a short while after going to ignition off and so my original thought (which I didn't mention) was OP really wouldn't see 0.78AMP draw after say 5-10 minutes after entering ignition off state. Albeit you're correct. 0.78 is very high for a vehicle in the true "off state."
    – Kilo
    Oct 14, 2013 at 17:23

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