[arudlang]

It sounds like something is wrong with whatever type of regulator this car uses to control the alternator, OR the alternator itself is bad, but I don't know why or how the alternator could work sometimes and not others which is why it feels more like a regulator.

Older cars the regulator was often a part of the alternator itself and it decided on its own when the system needed more current to put charge into the battery or power the car's electronics. With these ones I don't know, maybe the PCM uses sensors and a shunt to more precisely control the alternator's output to increase economy. The more amperage demanded from the alternator the harder it turns, since it is converting mechanical energy from the belt drive into electrical energy. It can take upwards of 3-6 HP to spin an alternator at full load so any time full load isn't required the regulator should ease off (I think), but I've never seen my voltmeter on my dash read less than 14.3-14.7 volts while driving.

The alternator should always be putting out some current, as far as I know. The running voltage should always be 14.3-14.7 the only thing varying would be how many amps is being drawn depending on load and battery SOC (state of charge).

So thats why it seems like its either a regulator of some sort or one of the voltage/current sensors could be providing bad data confusing the regulator too I supposed. Probably start by checking all wires from the battery and alternator area, I've found chipmunk chew marks under my hood on occasion.

If you have AlfaOBD it should have a bunch of electrical info it can plot and log during a test drive.

 

[arudlang]

seems odd that voltage did not drop on start up ...

I don't think mine drops either. Its probably either

1) The update is so slow on that gauge that its already started before it updates, or
2) Perhaps more likely, its showing the voltage of the small battery only during startup and not the larger cranking battery.

I skimmed over the annoying extra complexity of having two batteries in my earlier post but these do have two batteries. There is a solenoid that couples and decouples the two batteries in parallel based on computer command, I don't really understand when it connects them and when they are separated, but I am pretty sure the solenoid is off/batteries separated during engine cranking. Probably why the gauge on the dash doesn't drop.

So if you do test with your multimeter, I would expect the big battery to drop during cranking and the small one to stay level. If you have a continuity tester mode you can also test when that solenoid is on/off, its right near the two batteries can't miss it.