Mercedes-Benz W210 charging fault and battery/alternator warning
W210: what does the battery/alternator warning or Visit Workshop mean?
The message tells you that the battery is not charging or there is a fault in the electrical circuit. The cause can be the alternator, but just as well a blown fuse, a poor earth connection or a weak battery. The fault can also show up as a starting problem or limp mode.
What is the normal charging voltage of the W210?
Measure the voltage at the battery terminals. With the car off it is about 12.6 V, and exactly 12 V is too little. With the engine running the reading is about 14 V, and a small variation is acceptable. It must never be below 13 V. A weak battery can even lead to the engine stalling, because the electric feed pump needs current.
What is checked before replacing the alternator?
First check the earth lead between the engine and the body and the alternator earth, the fuses in the engine bay and the power supply connections, which can be corroded. Also measure the battery. After these, suspect the alternator, whose regulator, diodes, bearings or pulley freewheel clutch may be broken.