W212 Taxi alternator failed and stopped

Hi, last week I had to pick up a customer in a 100 km away place. During the drive the red battery message came. After 30 minutes came a message “Unvoltage engine start” although the car was still running. On the way back looked grasped all the symbols like ESP ABS AIRBAG PRESAFE etc. and after 10 minutes was finished. Was towed to the nearest Mercedes service and got a rental car, this went via Mobilo service. The next day came d he bill = alternator 800,00 Euro + 500,00 work wage. Proud 1300,00 Euro. So since prepared for such costs and possibly replaces the alternator prematurely. Symptoms were that the battery lately made for example after an hour did not want to start at the stop or from time to time came to this battery symbol in the display, in the cold state in the morning had easy difficulties to start. Kilometer level approx. 240 000 Km