A great perplexing electrical drain challenge .

Either you have no idea what you're doing or you were very tired when you wrote this up...

A 12v battery powers all the aux circuits in the car. Of course it is "live" when the car is off. It powers the radio to keep your presets. It powers the instrument cluster so it knows how much fuel you have and what your trip meters read. It powers the sensors in the windows to know the auto-stop limits. It powers the key fob computers to know when you're approaching the car or even when you press the button on your fob. It powers lots of things.

So having a 12v reading on a vehicle that's off is not a "drain" that's normal. Additionally a "drain" would imply current. If you're looking for phantom draw you should be measuring Amps/Milliamps in a series connection through the DMM as an ammeter.

If you're just measuring battery voltage a 12v reading on a 12v battery is dead. It should be closer to 12.8v. If your battery is actually 12v, then go buy a new one, that one is dead.

 

To put it a different way:
Your test method is invalid.
To BE valid, the meter needs to be set to measure current not voltage.

If old and weak enough, even the tiny little "normal" drains when sitting will cause the battery to go dead rather quickly.

Get the battery tested.
And if it is over 4 years old, get a new one.

 

Welcome. Forgive me, but I really did chuckle out loud a bit when I read @2k1Toaster's first line. There is no such thing as a 12V drain on the negative side. It would violate the laws of physics.

Your readings are perfectly normal and are exactly what I would expect except that I would have been afraid of burning out the meter if the current was much higher when connecting it in series and set to measure volts. Doing that more than once is how electrical apprentices flunk out of school. You never insert a meter set to volts into a circuit like that. If you had set it to amps, though, you would have seen that you didn't have a short. You had a very small load. Probably a tiny fraction of an amp.

When the car is off, there is a boatload of stuff still using power. If you had pulled all the fuses at once, you might have gotten a zero reading. As it was, when you pulled the negative cable off the battery, you shuff off everything. When you connected the meter in series between the battery and the ground cable, you closed the circuit again with all the current going through the multi meter.

As to the battery going dead, is this car new to you? Not knowing who tested the battery and how, it's hard to say from here if the battery is really good or not. If it really is good, it sounds like something has been installed that's connected to a voltage source that's not shutting off with the car.

 

Well, .82 is what I'd call more of a sizeable fraction of an amp. More than I would expect with the car quiescent. I would kind of expect at least one zero to the right of the decimal point....

Maybe there is something drawing more current than expected.

 

820mA (if measured accurately and with an accurate meter) is not unheard of if something is happening. For example just being near the car it could be priming brakes which is many many amps. Or doing communication with the key fob. Or all the doors could be open so the dome lights and hatch lights are on, etc.

 

0.82 A is about 10 watts out of that 12v battery, so if that is really the quiescent load you're getting, I'm not surprised it's draining overnight. But I would keep that ammeter hooked up and visible through a closed window and check it a few minutes later (without the smart key, to avoid the interior lights coming on.) If it's still that high, then try your fuse-pulling sequence until you see a drop, realizing that the small monitoring loads will always draw a few tens of milliamps as 2k1Toaster said.

(BTW, jerrymildred is incorrect about a voltmeter getting damaged by measuring in series with a circuit. It's the oppisite thing: An ammeter can get damaged if placed ACROSS a raw power source like a battery.)

 

This link might be helpful:

Dead Car Battery- How to Test a Car Battery

 

the pollution check must draw some energy

 

what we don't know yet: 12v measurement at night, and in the morning

 

Any sign of small rodents in the cabin or under the hood, suckers chew wires and wires short, it the 12v goes ded in a day, it's a ded short.
Or a ded 12v.

 

It most certainly can get damaged that way, but hopefully the fuse will protect it. And of course, if you have it set for 40A and run 100A through it, that will also damage it or blow the fuse. Both mistakes can blow the fuse or worse depending on the amperage. As an industrial electrician I've seen it happen.

 

I chuckled too......at your post.
Circuits are closed loops.
What goes out the positive MUST come back into the negative.
You can measure the current flow anywhere in the loop.

 

But it is WAY high if nothing is really happening.
Doing his fuse test while watching the current flow should show what is causing the draw.
But I suspect that if the ammeter is connected and then the car is left completely alone with no FOB present for an hour or so, the drain will drop to .20 or less, which would be normal.
My money is still on a weak battery.

 

Very likely, but if he tries it out, he'll have a learning experience that might be useful someday. And won't be guessing.

 

Just signed up and trying to ask a question. Just bought a 2008 Pius and daughter was driving it home was stuck in stopped traffic for an hour and half due to wreck. When she got home and I got in car red triangle on and check engine lite. I had her turn off and turn back on and had a single bar. Drove around for a while and went back to 6 bars green and no triangle or check engine? What do you do if in traffic like this? Thanks

 

Nothing ... the car takes care of itself in traffic like that, or any other kind.

Was your daughter doing anything in particular with the car during the time she was stuck in stopped traffic? She didn't shift into N, did she? That's a way to drain the battery.

If you're lucky, whatever trouble codes caused your warning lights to come on will still be retrievable by Techstream as historical codes, and then we'll be able to start guessing what happened to the car. If you're not lucky, they're gone, and we'll have to wait until it happens again before getting any further,

 

This is how I would measure amps, not volts. Try that?