Dashboard and COMAND showing different battery voltage

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Stratman

MB Enthusiast
Joined
Jun 15, 2003
Messages
5,820
Location
Sunbury
Car
W203 C200 CDI '04Estate
Because I now do mainly short journeys I like to keep an eye on the battery voltage. I normally use COMAND's 'three finger salute' to display it but when I use the dashboard to show the charging voltage it's about 0.7 volts higher than COMAND. The car shows 14.2, COMAND 13.5 or thereabouts. Which do I believe and why?
 
Are they reading the values from different places?

14.2V sounds like an alternator value and 13.5V sounds like a value taken further away with consequent voltage drop.
 
I've noticed this on my W209 as well. The only one I *really* believe is putting the voltmeter across the battery terminals. A touch tricky while the car is in motion though.
Failing that, the voltage on the cigarette lighter socket seems accurate.

Your car probably has a 'smart regulator' as well. The apparent voltage will drop as the controller senses a lack of load - e.g. stationary in traffic, few consumers and a healthy battery.

Ian.
 

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