Take the 2-minute tour ×
Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It's 100% free, no registration required.

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?

share|improve this question
1  
Do you have a security system that could be triggering something, and waking the car up? –  FossilizedCarlos Jun 19 '12 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 '12 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 '12 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 '12 at 12:43
    
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 '13 at 14:54

5 Answers 5

up vote 5 down vote accepted

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.

share|improve this answer
1  
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 '12 at 12:45

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.

share|improve this answer

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.

share|improve this answer
1  
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 '13 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 '13 at 17:23

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

share|improve this answer

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.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.