Battery drain - normal resistance across terminals?
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Joined: May 2010
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From: Vic Australia
BUT left for a 10/15 days,in cold unheated garage, battery measures 12.97/12.98, close to 13V !!
now how does a battery gain voltage when NOT in use, that ever so slight increase makes my Jag V12 start quicker, gages come up quicker, response seems better?
i,m thinkin maybe more spark energy also!
then i drive away for some road time , come back it measures 12.65V, and the cycle starts over!
I LIKE IT , SO BE IT.
times they are a-changing??
now how does a battery gain voltage when NOT in use, that ever so slight increase makes my Jag V12 start quicker, gages come up quicker, response seems better?
i,m thinkin maybe more spark energy also!
then i drive away for some road time , come back it measures 12.65V, and the cycle starts over!
I LIKE IT , SO BE IT.
times they are a-changing??
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Member
Joined: Jan 2020
Posts: 54
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From: London
You guys were right, I did in fact measure only 4mA of draw despite measuring only a couple of ohms across the terminals. Mind you, this is after the car has (effectively) been disconnected by the battery going flat.
I originally posted because the car wouldn't start and I couldn't figure out why. I went on hols while the battery conditioned; when I came back, the issue was gone and the car started fine. I still had 2-3 ohms acorss the terminals, but the voltage held comfortably above 12V while the car sat for days at a time.
Last night it happened again - the battery dropped to 0.2V, and I doubt I'll get it back from there. New one on order.
Both times this has happened, the car stood in the rain overnight - normally it lives in a garage. Could be coincidence.
Now I realise that all my troubleshooting by pulling fuses was useless, because I was measuring resistance and not current. <sigh>
Doug:
> I would suggest the additional step of connecting the battery, running the engine and operating all components, let the car sit for 10 minutes, then, without ever disconnecting the battery, connect your meter, set to measure a 10 amp draw, then remove the battery cable.
Is there any value in doing this without running the engine? I have a leisure battery that'll supply maybe 40A, but nowhere near enough to crank. I'd like to see if I can find the gremlin before it disappears again.
I originally posted because the car wouldn't start and I couldn't figure out why. I went on hols while the battery conditioned; when I came back, the issue was gone and the car started fine. I still had 2-3 ohms acorss the terminals, but the voltage held comfortably above 12V while the car sat for days at a time.
Last night it happened again - the battery dropped to 0.2V, and I doubt I'll get it back from there. New one on order.
Both times this has happened, the car stood in the rain overnight - normally it lives in a garage. Could be coincidence.
Now I realise that all my troubleshooting by pulling fuses was useless, because I was measuring resistance and not current. <sigh>
Doug:
> I would suggest the additional step of connecting the battery, running the engine and operating all components, let the car sit for 10 minutes, then, without ever disconnecting the battery, connect your meter, set to measure a 10 amp draw, then remove the battery cable.
Is there any value in doing this without running the engine? I have a leisure battery that'll supply maybe 40A, but nowhere near enough to crank. I'd like to see if I can find the gremlin before it disappears again.
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Joined: Sep 2016
Posts: 4,277
Likes: 1,314
From: New York New York
You guys were right, I did in fact measure only 4mA of draw despite measuring only a couple of ohms across the terminals. Mind you, this is after the car has (effectively) been disconnected by the battery going flat.
I originally posted because the car wouldn't start and I couldn't figure out why. I went on hols while the battery conditioned; when I came back, the issue was gone and the car started fine. I still had 2-3 ohms acorss the terminals, but the voltage held comfortably above 12V while the car sat for days at a time.
Last night it happened again - the battery dropped to 0.2V, and I doubt I'll get it back from there. New one on order.
Both times this has happened, the car stood in the rain overnight - normally it lives in a garage. Could be coincidence.
Now I realise that all my troubleshooting by pulling fuses was useless, because I was measuring resistance and not current. <sigh>
Doug:
> I would suggest the additional step of connecting the battery, running the engine and operating all components, let the car sit for 10 minutes, then, without ever disconnecting the battery, connect your meter, set to measure a 10 amp draw, then remove the battery cable.
Is there any value in doing this without running the engine? I have a leisure battery that'll supply maybe 40A, but nowhere near enough to crank. I'd like to see if I can find the gremlin before it disappears again.
I originally posted because the car wouldn't start and I couldn't figure out why. I went on hols while the battery conditioned; when I came back, the issue was gone and the car started fine. I still had 2-3 ohms acorss the terminals, but the voltage held comfortably above 12V while the car sat for days at a time.
Last night it happened again - the battery dropped to 0.2V, and I doubt I'll get it back from there. New one on order.
Both times this has happened, the car stood in the rain overnight - normally it lives in a garage. Could be coincidence.
Now I realise that all my troubleshooting by pulling fuses was useless, because I was measuring resistance and not current. <sigh>
Doug:
> I would suggest the additional step of connecting the battery, running the engine and operating all components, let the car sit for 10 minutes, then, without ever disconnecting the battery, connect your meter, set to measure a 10 amp draw, then remove the battery cable.
Is there any value in doing this without running the engine? I have a leisure battery that'll supply maybe 40A, but nowhere near enough to crank. I'd like to see if I can find the gremlin before it disappears again.
Close all doors, off all lights, key OUT of ignition all together.
Place the battery IN the car. Connect the positive lead from car to the battery. Leave negative cable from car disconnected from battery. Set DMM to amps. Highest amps setting to begin... Place your volt meter between the battery (positive probe on negative battery terminal with clamp) and a solid chassis ground (negative DMM probe on chassis) and see what you DMM reads. If the reading is low dial down your DMM to low settings to get an accurate reading with significant figures.
Begin to CAREFULLY go around and check fuses, relays, light fixtures, dials etc... Car as OFF as possible.
If you run a lot of amps/current to the car you will get your DMM...
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Joined: Sep 2016
Posts: 4,277
Likes: 1,314
From: New York New York
If ya really get frustrated (I'm imagining you already are - I would be) and ya NEED to create conditions like rain,,, grab a hose and spray all over it, spit on it, **** on it,,, and all that stuff... Isn't it amazing how crazy a car can make ya? Lol. Been there,,, am there. Omgoodness
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