Parasitic battery drain
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Freshman User
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Parasitic battery drain
I've tested the battery at 13.1V. I did test it after a drive so that may have made the test inaccurate. With both doors closed and key out of the ignition. I got .013A which I think is 13milliamps. I thought that low of a draw was maybe from some atmospheric condition. runs fine for the rest of the weekend. Drove it this morning to the gym. Came back out, 5 min with key in the ignition; battery is just strong enough to turn the engine over once nothin more. Can current be drawn with the key in the ignition? I am using a smaller battery but it still usually works fine. Any suggestions?
Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
Likes: 78
From: NE Texas
quick test - with everything turned off, disconnect your ground clamp from your battery and put a test lamp between the battery post and clamp - if it glows at all, you verified a drain. Then start disconnecting fuses - when the light goes out you have an idea which circuit the drain is in and can start more detailed diagnostics.
Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
quick test - with everything turned off, disconnect your ground clamp from your battery and put a test lamp between the battery post and clamp - if it glows at all, you verified a drain. Then start disconnecting fuses - when the light goes out you have an idea which circuit the drain is in and can start more detailed diagnostics.
I think you may have at least two separate problems, a bad battery and a low amp "short".
Have a good load test done on the battery first. A low draw as you describe wouldn't / couldn't drain a battery in 5 minutes.
An alternator with a weak diode will create a draw. Isolate the alternator from the truck and see if that clears the draw.
I have encountered similar low amp draws from corroded door jamb switches. It was a high resistance (low current flow) path to ground.
Another low amp draw could be your radio. If you have an aftermarket radio with a memory, or a factory radio with a clock, you will have a draw.
In either case, pulling fuses one at a time, as Houston Dave suggested, will help identify the problem circuit.
Hope this helps. Good luck.
Cargo Master
Joined: Apr 2009
Posts: 3,038
Likes: 4
From: South west Idaho
Pulling fuses never helped me , i did it several times over a few months then some body told me to remove the bat wire to the alt. I did that and let it sit for 2 weeks longer than i would let it sit before . It never killed the battery so i installed a new alt. and it's never went dead going on 5 years now. So pulling fuses never made that show up , the alt. had a weak diode and was draining it down slowly over a few days.
Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
Pulling fuses never helped me , i did it several times over a few months then some body told me to remove the bat wire to the alt. I did that and let it sit for 2 weeks longer than i would let it sit before . It never killed the battery so i installed a new alt. and it's never went dead going on 5 years now. So pulling fuses never made that show up , the alt. had a weak diode and was draining it down slowly over a few days.
Jim is correct.
Pulling fuses won't identify a bad alternator, since the wiring from the alternator to the battery isn't fused.
That is what I was trying to say in my poorly worded previous post, when I said "isolate the alternator from the truck".
Postmaster
Joined: Nov 2011
Posts: 2,553
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Key in ignition has been known to affect draw. It shouldn't, of course, but sometimes does if there is an issue with the switch.
In general, 20 mA draw is considered good and 50 mA marginal. It would take a lot more than 50 mA to pull down the battery while you were at the gym. Either 1) you have more draw in certain situations (eg key in) or 2) the battery is shot as mentioned in previous posts. 3) Alternator is bad as mentioned in previous posts.
Battery can be tested or for a DIY check, charge it up then pull the negative battery cable while it sits for a while. If it starts fine with cable re-connected, probably a draw. If not, probably the battery.
In general, 20 mA draw is considered good and 50 mA marginal. It would take a lot more than 50 mA to pull down the battery while you were at the gym. Either 1) you have more draw in certain situations (eg key in) or 2) the battery is shot as mentioned in previous posts. 3) Alternator is bad as mentioned in previous posts.
Battery can be tested or for a DIY check, charge it up then pull the negative battery cable while it sits for a while. If it starts fine with cable re-connected, probably a draw. If not, probably the battery.
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Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
I agree with most of what Blue and White says, above, but you need to take your testing a bit farther.
A marginal battery can cause problems and can be hard to detect without putting a load test on it.
A cheap and easy load test can consist of nothing more than leaving you headlights on, engine off, for 5-10 minutes and then starting the truck. If the rig doesn't start, or cranks slowly, you have a problem with the battery.
A lot of auto parts stores have a load tester that works in a similar fashion, only they put a much greater load on the battery for a shorter time and can check battery voltage during the load test.
A marginal battery can cause problems and can be hard to detect without putting a load test on it.
A cheap and easy load test can consist of nothing more than leaving you headlights on, engine off, for 5-10 minutes and then starting the truck. If the rig doesn't start, or cranks slowly, you have a problem with the battery.
A lot of auto parts stores have a load tester that works in a similar fashion, only they put a much greater load on the battery for a shorter time and can check battery voltage during the load test.
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Laughing Gas
Joined: Aug 2010
Posts: 896
Likes: 55
From: Bothell
I just went through this with my truck... turned out to be an internal short in the battery. Battery has 600+ cca after driving/charging. Two hours later with ground and positive disconnected it was down to 300ish cca.
If you need an excuse to buy a new tool these guys make good battery load testers. I have the BA7 and it's been great, lets you know what shape the battery is in and with timed testing intervals it will let you know if the battery has an internal short (ie dead battery). It also tests the charging system too. Seems to run about 60$ or so.
Battery Testing - BA Series System Testers for Detailed Data | Call us at 1-800-328-2921 | Clore Automotive
If you need an excuse to buy a new tool these guys make good battery load testers. I have the BA7 and it's been great, lets you know what shape the battery is in and with timed testing intervals it will let you know if the battery has an internal short (ie dead battery). It also tests the charging system too. Seems to run about 60$ or so.
Battery Testing - BA Series System Testers for Detailed Data | Call us at 1-800-328-2921 | Clore Automotive
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Freshman User
Joined: Sep 2012
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went to the gym today again with the key out but headlights were on 😳 battery went dead again. Got jumped off and went about my day just fine. Started up at work just fine as well and went home. I tested tested the load again and only got .03 mA. Started the engine, measured only 12.9V comin from the alt. Turned on the radio, fan and headlights, only 12.4V was coming from the alt. I disconnected the terminals. The engine died with the radio, fan and headlights on. I think it's the gym causing the problem 
maybe bad alt paired with a small battery is the problem. What am I suppose to be getting from the alt?
maybe bad alt paired with a small battery is the problem. What am I suppose to be getting from the alt?
Cargo Master
Joined: Apr 2009
Posts: 3,038
Likes: 4
From: South west Idaho
Your alternator can still charge but when it's parked a bad diode in it can drain the battery down. I think removing the battery cables while the engine is running may damage the diode . I know i had done that on mine a few years ago and that's when i started having troubles .
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
I just went through this with my truck... turned out to be an internal short in the battery. Battery has 600+ cca after driving/charging. Two hours later with ground and positive disconnected it was down to 300ish cca. If you need an excuse to buy a new tool these guys make good battery load testers. I have the BA7 and it's been great, lets you know what shape the battery is in and with timed testing intervals it will let you know if the battery has an internal short (ie dead battery). It also tests the charging system too. Seems to run about 60$ or so. Battery Testing - BA Series System Testers for Detailed Data | Call us at 1-800-328-2921 | Clore Automotive
Normally these units are connected directly to the battery posts to prevent any terminal corrosion or resistance from interfering with the accuracy of the test. This characteristic can also be used to test the overall quality of the cables and ground connections. With the negative end connected to say, a head bolt, or alternator bracket, a passing grade here shows good, low resistance in the starting and charging circuits.
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