Rahulio1975280C

About a year ago, I was driving on the highway and got the "Alternator/visit workshop" warning on the dash. After some research on the issue, it seemed like a lot of people had success changing the voltage regulator on the alternator instead of replacing the entire alternator. I did that too, and it seemed to have solved the problem.

However, yesterday, I had an issue with a dead battery after driving to a place about 25 minutes away (mostly highway). When I came back to the car after about 30 mins, the battery was dead. My battery was 6 years old, so I decided to replace it. In the diagnostic menu that the C55 has (pit key in ignition, turn key to first position, press cluster knob in 3 times) there is a voltage reading that you can get when the car is off and on.

Before starting my car, the UB voltage reading is 12.7V.
When I start my car it rises to 14.5V
As I driving around town, it steadily drops to 13.5V, but does not seems to drop below that. (Headlights on, ac on, radio on, heated seats off)

Does anyone have familiarity with this behavior on the C55? I imagine it applies to most M113 powered cars, but thought I would ask people with the same car, first. Below are images taken yesterday after installing a new battery.

Plutoe

What you have observed and experienced is not germane to your vehicle. Its physics and applies to all battery charging systems. If your battery will not take a charge at some point it wont have the charging amps to engage the starter. You did what most folks would do install a new battery. Now if you have new battery and a faulty charging system at some point it wont have the starting amps to start the car.
You are not alone in the world!!