I have been having problems lately that I narrowed down to either the alternator or the battery so I replaced both of them and the problem still persists. I went back to autozone and talked with one of the guys who actually knows something and he found there was a .5 amp draw on my system and said that could drain a battery over night pretty easy. I dunno if I believe him so Im asking you guys.

If this is significant then how might I go about finding where the problem is? I dont have any aftermarket audio equipment.

 

A .5 amp draw would take ~150 hours to kill an average 75 amp car battery.

 

Well I had been letting my car sit for 12 hrs at a time is all and it wouldnt start.. just get 1 click out of the starter. If I jump it however, then it starts just fine.

I bought a multimeter today and found there is only .02 amps flowing out of the battery so I dunno where the autozone guy got his readings. I am suspecting the draw may have been coming from my electric fan splice I made in the harness for my fan switch. When I touched them I heard the damn relay click on and the fans turned on for a second. After taping up the splice better I couldnt get them to do it again so I may have fixed the problem for now. Unfortuantely I did all this BEFORE running to buy that multimeter.

 

I am having this EXACT problem, if I figure it out before you I'll post about it. PLEASE post it if you figure it out before I do.

 

Did you check to see if there is any current draw from the battery over .02 amps? I know my problem isnt the battery or alternator at this point so Im leaning towards a bad circuit somewhere.

 

The typical car will draw 6-10 MILLIamps while stopped with nothing on. That is .006-.001 milliamps. Some newer cars with lots of electrical do dads will be slightly higher. Anything significantly higher than this is probably something going wrong. Make sure you are taking your readings in the appropriate spots, as current measurements can be tricky.

Also, taking straight discharge rates and rated capacity does not give a truly accurate reflection of expect battery life. A battery will discharge more or less actual amperage depending on the conditions, such as current discharged/charged status, discharge rate, battery temp, etc.

Jonota

 

I had a friend at the battery taking readings while I was pulling fuses. The only thing that made a noticable differance was the intrerior light. Nothing else.

 

The question was HOW was he taking the readings. Just hooking up to the battery + and - won't do it correctly if I remember right. You need to disconnect one of the cables, the connect your multimeter between the battery terminal and the disconnected wire... although I'm pretty tired right now I'm not sure I'm right.

 

I'm not doubting you, simply trying to understand. How would there be a complete circuit if you did not have the + and - connected?

 

the ammeter (amp-meter) must be PART of the circuit to measure correctly (in my example, the meter completes the circuit between the battery terminal and the battery cable.... if you take it on the battery terminals it will only read that amount of current that goes through the multimeter instead of the total current. Hence since the ammeter is in PARALLEL with the TRUE circuit, it will only show a fraction of what the true amperage draw is.

Jonota

 

I had an '89 Blazer with one of those under hood lights with a mercury switch that was supposed to turn the light off when the hood was closed. Well, it was faulty, and in the winter, if I didn't drive for a couple of days, it would drain the battery enough to where it wouldn't have enough juice to crank the engine. Took the bulb out, and the problem went away. Battery was a couple years old.

 

I disconnected my NEG battery cable and used my multimeter to make a bridge between the battery terminal and the NEG junction on the shock tower. I couldnt keep a connection on the cable with those damn probes and the readings were identical at the junction so I used it instead.

 

It really depends on what accessories you've added, but on average, anything above 90mA total would be a significant drain. My car will kill a battery within 2 weeks due to the aftermarket alarm in it. Another thing to consider is, that if your battery has been completely drained in the past, it'll likely NEVER be up to par again, even if you repeatedly slow charge it. I've gotten in the habit of just replacing the battery once it's been drained too far.

What you need to do is connect the meter in series with either of the cables, then systematically unplug one fuse at a time and see what is causing the drain.

 

UPDATE- Found the problem. The car is not a daily driver so it's been sitting for 3 days without being started. I went out to see if it still had some juice in the battery and much to my surprize it did! I put the key in turned it over, and it fired right up. I have only done ONE thing different, I unpluged my radar detector. If the problem comes back I'll let you know.


P.S. It was a VERY SMALL draw according to the volt meter.