Voltmeter reads low compared to battery until a few seconds after the motor is started?

[007 jbnd5]

I have a weird situation that’s confusing me on my ‘95 Jeep Cherokee Sport. The voltmeter reads anywhere from 9-11v when the key is in the on position but the engine is not running. When checking the battery with a multimeter it sits at about 12.5v. A few seconds after starting the engine the voltmeter jumps back up to the ~13v that the battery sits at while the engine is running. Everything I’ve tested has 12+v going to it without the taking apart the dash.

I also have the 41 code which everything I’ve read is about the alternator and it needing to be replaced. Could this all be related to the alternator or is there something weird happening between the ignition and voltmeter ground?

 

[lawsoncl]

I would start by cleaning up the battery terminals and checking whether the cables are rotten inside. Also note that the dash voltmeter isn't all that accurate.

 

[007 jbnd5]

I’ve checked the voltage in several places and gotten 12+v so I don’t think it’s the termials. The termials are really quite clean since the battery is less than a year old as well. Cables being rotten is possible. The voltmeter isn’t super accurate but it’s never read low enough to cause the check engine light to turn on while starting it till the last month.

Another observation is if it sits for several hours the voltage reading is closer to 9 when I turn it on but leave the engine off. After 30 seconds the voltage increases to about 11v and settles there while the battery is 12.6v with the engine off. I do wonder if the voltmeter is just going bad also.

 

[techno]

A good battery usually sits at about 2.1 +/- volts per cell. A good charge rate will be about 2.3 volt per cell. There are 6 cell in a 12 volt battery. Your battery is in good condition.
For my AGM batteries, I aim for 2.35 volt per cell which put the charging at 14.1 volts at the battery, and 0.2 volt higher when it is cold outside.

 

[Unclewolverine]

The gauge is notoriously inaccurate, but check your power at your accessories. The contacts in the ignition switch build up resistance over time. I have a 12v power point directly to the battery and the factory one that runs through the ignition switch, there is over a volt difference between the two. With every accessory running my battery gauge reads almost to the red, but I'm still showing 13.5 at the battery.

 

[techno]

The gauge is notoriously inaccurate, but check your power at your accessories. The contacts in the ignition switch build up resistance over time. I have a 12v power point directly to the battery and the factory one that runs through the ignition switch, there is over a volt difference between the two. With every accessory running my battery gauge reads almost to the red, but I'm still showing 13.5 at the battery.

100% accurate. Thats the reason I check voltage only at the battery. The gage however gives an idea as to whether or not the alternator is working but not the system voltage.