Car Battery Voltage

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I recently bought a little gadget that plugs into a fag-lighter socket, and has a digital display of Voltage.

When I turn the key to "Acc" with engine stopped after standing for 24 hours or more, it displays 11.1V which increases to 14.4 when I start the engine.

This is not a no-load voltage, because the A/C fan, auxiliary coolant pump and various electronic services come on as soon as the key is turned. The battery is very large, 90AH.

Is that normal for a battery in good condition? 11.1V seems rather low.

Edit
having researched this further, all the tables I can find for voltage:battery state of charge are at no-load, so I will try my DMM on the battery terminals with (almost) everything off and see how that compares to the gadget reading on ACC. It looks like 12.5v would be an reasonable no-load voltage in winter, and 12.6 in hot summer.
 
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As you say would expect near 12.6 volts for a decent battery, maybe the gadget is a little out as i would not expect it to dip that low.
 
'mmm

fully charged batt, left car untouched for 24 hrs, no-load at batt terminals was 12.63, temp about 8C, so probably in good condition.

however the gadget momentarily showed 12, dipping to 11.8 steady. Unfortunately it is impossible to get a no-load with the key in the ignition, the car has too much automation. I will try to remember that an indicated 11.8 is fully charged.
 
I would think that is probably about right, if you only had 11.8 volts with no load I would suspect the battery but I think you would have difficulty starting the car if that was the voltage displayed with no load.

Peter
 
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John, don't know if it's the same or similar gadget to the one I bought (very cheap off Ebay?) but with key in position 2, with no accessories on, mine was showing anything between 11v and 13v. Proved it to be very inaccurate using a voltmeter and so is now residing on the Council tip.
 
hmm, I'll see if I can poke my DMM probes into the faglighter socket without fear of shortcircuit.

the reason I got the gadget was to tell me if the batt was due a topup charge in winter, so if it can't do that, it belongs on the tip. Yes, it was cheap on fleabay.
 
If your meter is reading 14.4 volts with the battery charging that is pretty well spot on so I would say your meter is OK - unless its very non linear.

Peter
 
The wee lassie in China was probably building fireworks before voltage indicators, so you need a bit of tolerance.

You could connect a flying lead to the middle terminal positive, and another to the outer terminal negative, on the voltage indicator. Connect directly across the battery?

If you look at the packaging her E-Mail address might just be on the back so you can contact her, but I doubt it ..............
 
'mmmm

I fully charged it on 1st Jan, it has been standing, unused, for 40 days with just the alarm and clock drawing power, and was down to 11.6v today when tested with DMM at the battery terminals (the alarm honked when I opened the boot, but I did not try to start the engine).

I don't know how long a battery ought to keep a charge when idle.

Does that sound reasonable?
 
Years?? It's done very well indeed!
Only expect a new or almost new battery to be reading over 12v after standing for that length of time.
After 7 or 8 years, they are on borrowed time.....a few years ago, they didn't last anywhere near as long as that.
John :)
 
it might be younger, but I can't see a date label on it. It looks very clean (is in the boot)
 
There's often a first charge date somewhere, but for sure, it's been a quality battery right from the start.
It isn't a Yuasa, is it?
John :)
 
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