Battery Showing 15 Volts??

[dilligaf76]

Can’t work out why a cars 12 volt battery is showing nearly 15 volts with a multimeter when the car isn’t even running.
I then started the car and the multimeter went up to 17 volts?

[No ideas for a name]

dilligaf76 said:

Can’t work out why a cars 12 volt battery is showing nearly 15 volts with a multimeter when the car isn’t even running.
I then started the car and the multimeter went up to 17 volts?

Most likely the multimeter needs calibrating.

[dilligaf76]

Actually thinking about it I measured the volts after it had been on charge for an hour or two. Would this be why is was showing a high voltage even though the charger was disconnected?

[finlo]

Most likely, the charger has to be several volts higher than the battery it is charging so you could see a higher voltage initially.

[119]

I’ve only ever seen them hovering within the 14v range or below if the battery or alternator is on its way out.

[InitialDave]

My multimeter gives duff readings like that when the internal battery is getting low.

[shtu]

Check the voltage of an AA battery and see what it says.

[E-bmw]

As above, your meter is definitely reading wrong.

12v battery should be around 12.6v if in good condition & fully charged.

[dilligaf76]

Okay thanks, I’m gunna have to test some other batteries and maybe get a different multimeter, thanks again for everyone’s input :-)

[dilligaf76]

Okay thanks, I’m gunna have to test some other batteries and maybe get a different multimeter, thanks again for everyone’s input :-)

[GliderRider]

InitialDave said:

My multimeter gives duff readings like that when the internal battery is getting low.

Just changed the battery in my multimeter today for this very reason, plus the low battery indicator showing...

[dilligaf76]

My multimeter hasn’t got a low battery indicator. Did it read different after you changed the battery and show different results when testing after?

[GliderRider]

dilligaf76 said:

My multimeter hasn’t got a low battery indicator. Did it read different after you changed the battery and show different results when testing after?

Yes, the multimeter showed implausibly high readings before changing the 9V battery, and back to sensible readings afterwards.

I scratch the date on the 9V batteries when I install them. The one I removed went in in 2012.

Edited by GliderRider on Thursday 1st February 09:30

[tux850]

dilligaf76 said:

My multimeter hasn’t got a low battery indicator.

That's no problem... Just pop the battery cover off and measure the voltage of the installed battery using the meter itself.

(Actually, joking aside if it reads more than 9v - assuming a PP3 - then there's your issue confirmed!)

[dilligaf76]

Well I measured the voltage of the old PP3 battery with a new one installed and it was bang on 9 volts.
I then measured the same old PP3 battery with a new multimeter I received today and this time it said it was 8.65 volts.
So which one of the two multimeters should I believe?

[tapkaJohnD]

A lead-acid battery comprises six cells each of which deliver 2.2V at best, 13.2 overall.
It's not physics-ly possible for it to deliver more!

As Scottie might say, "The DiLithium crystals wll nae stand it, Capn!

[keeling54]

Run it down to your nearest Halfrauds, they'll have a battery tester which give you the correct figure.

I remember my old C class hit 18 volts when the alternator regulator went, it blew something in the engine management system which I couldn't fix.