Dash Voltage reading vs Multimeter at Battery

[Maximus Gladius]

Can someone (or many) explain why there are two different voltage readings when checking what the batteries are reading?

Thanks to @Stan H for mentioning battery voltage issues,…it made me check mine!

Engine off, dash says 12.1 and the multimeter says 12.34v. I’m confused. (This happens often)

The drive to work this morning, the alternator didn’t charge lower than 14.2 the whole time.

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[CyberShanks]

No idea on the discrepancy between 12.1 and 12.34, but the 14.2 is coming from the alternator due to the engine now running.

Jim

 

[Stan H]

And these are my readings . Which is what Prompted @Maximus Gladius to check his .
Can't wait for you all to explain how that can be.

I did and IBS reset after Driving to work . It is charging at 14.1 for a long time just dropped to 14.0 letting it charge last night. Just didn't have time to reset before taking off. Near 2 hr. Drive there. @ ShadowsPapa @Charles 236 @Hootbro What do ya think?

 

[Jaxmax]

I would think you would get a higher reading right off battery posts , no connection loses, no voltage drop on wires to dash volt sensor. Calibration of multimeters can also be part of it ,either way. Stan I’m more concerned that you had it charging over night at 14 volts? Is that off a separate battery charger. I dabble in electric have a pretty large crew all using expensive Fluke meters and calibration is done with factory but really don’t find issues, and really we don’t calibrate as often, but guys do check across other guys meters when doing detailed work…..Jack

 

[Stan H]

I would think you would get a higher reading right off battery posts , no connection loses, no voltage drop on wires to dash volt sensor. Calibration of multimeters can also be part of it ,either way. Stan I’m more concerned that you had it charging over night at 14 volts? Is that off a separate battery charger. I dabble in electric have a pretty large crew all using expensive Fluke meters and calibration is done with factory but really don’t find issues, and really we don’t calibrate as often, but guys do check across other guys meters when doing detailed work…..Jack

@Jaxmax no that is what it is charging at now . Over night I had a 4amp AGM12volt charger on it .. my writing skills leave to be desired

 

[Stan H]

I would think you would get a higher reading right off battery posts , no connection loses, no voltage drop on wires to dash volt sensor. Calibration of multimeters can also be part of it ,either way. Stan I’m more concerned that you had it charging over night at 14 volts? Is that off a separate battery charger. I dabble in electric have a pretty large crew all using expensive Fluke meters and calibration is done with factory but really don’t find issues, and really we don’t calibrate as often, but guys do check across other guys meters when doing detailed work…..Jack

@Jaxmax Would you suggest I get another multimeter and do a side by side comparison to verify the validity of the computation and calibration of the voltage meters and make a more rock solid assessment of the voltage

 

[Hootbro]

Instrument cluster voltage gauge reading gets it info from the PCM which monitors and acts as a voltage regulator for the charging system. It is going to show the system under load and not what is static at the battery. I would expect a few tenths difference between the two. Couple that also as mentioned with some tolerance stacking.

 

[Stan H]

Instrument cluster voltage gauge reading gets it info from the PCM which monitors and acts as a voltage regulator for the charging system. It is going to show the system under load and not what is static at the battery. I would expect a few tenths difference between the two. Couple that also as mentioned with some tolerance stacking.

So what your saying is that with engine off and key on that is is giving a reading under load ?

 

[Mr._Bill]

Fully charged, with everything off, the reading at the battery should be 12.8 volts. A reading of 12.3 shows a discharged battery of questionable health.

 

[Maximus Gladius]

So now I’m wondering why I don’t see the Captain America symbol @12.1v ?? I’m wondering when that gets triggered

 

[Maximus Gladius]

@ 12.1v

 

[Mr._Bill]

So now I’m wondering why I don’t see the Captain America symbol @12.1v ?? I’m wondering when that gets triggered

That comes when the Aux Battery fails the startup test. It may be in better shape than the Main Battery. Disconnect the Aux Battery Negative cable from the IBS to measure it.

 

[Hootbro]

So what your saying is that with engine off and key on that is is giving a reading under load ?

Basically, even with the engine off and in either run or acc, there is still vehicle electronics on pulling a amperage draw with corresponding voltage drop.

 

[Hootbro]

Need to quit looking into the "why" when noting is faulting.

 

[ShadowsPapa]

I would think you would get a higher reading right off battery posts , no connection loses, no voltage drop on wires to dash volt sensor. Calibration of multimeters can also be part of it ,either way. Stan I’m more concerned that you had it charging over night at 14 volts? Is that off a separate battery charger. I dabble in electric have a pretty large crew all using expensive Fluke meters and calibration is done with factory but really don’t find issues, and really we don’t calibrate as often, but guys do check across other guys meters when doing detailed work…..Jack

Yes - the cluster is reading through the IBS and other wiring. I'm not sure how totally accurate the IBS voltage reports are vs. a meter, but there can be variations just in meters (I have about 6, 3 of them digital, and I trust the Fluke over the others - but it hasn't been calibrated in a while, either)
One thing to be sure of - take the reading at the battery while the cluster display is on - if you hit the big button to turn things on, the draw from the electronics themselves increases and if you then shut it off and go measure the battery, it will be a big difference with the load of the display removed.

Not sure if the meter is being used to read the battery while the cluster is also on showing the voltage inside.

The voltage reading should be what the IBS is reporting. You can actually use JSCAN to see what voltage is being reported by the IBS.

In any case, anything under 12.4 is "time to charge batteries" territory.
I'd charge each battery independently, reset the IBS and see how the voltage holds on each battery as they sit after charging before reconnecting.

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