12.67 rested or higher is fully charged. When applying a charge the system should hit 14 plus but never over 14.8. This is boiling time.

As long as the system is putting more juice in than taking out it is okay but a good thing to remember is that with that low of voltage your amperage at idle is also very low. Add a blower motor, wipers and headlights and the system is very likely discharging at idle.

Add to that the fact that you just ran a full cycle on the glow plugs and short stop and go traffic in town could feasibly run your battery down too low to start the car...

I had a '73 Dodge and it had the worst charging system in the world. The voltmeter woudl drop to like 11 volts at idle.

You can test your charger by watching the voltage it is putting to the battery until it peaks. That is full charge as long as it is above 14 volts. Let the battery set for about 4 hours or apply a 20 amp discharge for 20 seconds to take off surface charge then check the battery. that is yoru battery t full charge. they all vary slightly. Gives you a pretty good basline at the current temp.

Lastly, voltage varies with temperature. Colder equals lower voltage.

Sorry to be so verbose. I own an RV and knowing your batteries in the winter are everything!

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique