1998 Mercedes E300 TD (W210) Battery light/Voltage loss while accelerating

What is your question?

Few weeks ago everything was fine with my 1998 Mercedes-Benz E300 TD (W210). I was on the way home on the highway and didn't realize I was I had accidentally bumped my shifter into third gear. Long story short the vehicle began to redline due to the high speeds; however, at the same time the charge battery light came on. I then shifted the vehicle into fourth and everything was fine. Now.. I've used the built-in multimeter via my radio and the battery reads 11 volts off and 13.3 with the alternator running. Also, if I accelerate the vehicle more than a slight increase, or go over 80kmh/2,000 RPM the volts drop from 13.3 to 11.6. I replaced the battery and the issue persisted. My concern is that it is my alternator/voltage regulator.. but the car runs perfectly fine (lights, windows, high-beams, etc.) Any help is greatly appeciated! Thanks!

What makes this problem better or worse?

Accelerating

How long has your 1993 Mercedes-Benz 300E had this problem?

a few weeks