12v Auxiliary Battery wile driving chart

It's less than a 1-volt drop, so I'd say you're fine. A tight scale like your chart can make any change look alarming. Of course if the aux battery is 9 years old you're living on borrowed time.

 

Looks good how old?

 

Test it with something like Solar BA9, with the car off.

And I'd second: if it's original battery, don't even bother testing, just replace.

 

That looks normal. Where are you measuring this voltage?

 

That was taken while driving, right? So the only thing it is showing you is the car's control strategy for the DC/DC converter output, where it sends 14-ish volts toward the battery initially to replenish a bit of charge, then relaxes to 13-ish for most of the trip to continue recharging at a more gentle rate. The return to 14-ish near the end of the trip wasn't part of my understanding of how the control strategy works, but it's more likely that I don't know all the rules than that the car is doing anything weird. Was that at the moment you parked at the end of the trip, by any chance?

Main takeaway: any such chart generated while the car is in READY is showing you what the converter is doing, not so much the battery; the converter is in control.

 

Voltage will drop from turning devices on such as headlights and car will run continuous tests checking things such as evap, hv bat and etc so there will be some lag but not enough to affect overall vehicle performance, unless 12v bat is going bad. Voltage will go up and down according to hv battery SOC also.

 

testing while driving is useless. check it with a volt meter after it has been off a few hours, then turn the headlights on and record the drop over time

 

+1