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Q: Alternator not charging battery a600

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I have a 01 mercedes s600 and when purchased the car the alternator was not charging the battery at idle but some at higher rpms. Purchased a rebuilt one from autozone and had it installed and still did not work. Just purchased a oem used alternator with 15k miles on it hoping this should fix the problem. Any advice?

My car has 103000 miles.
My car has an automatic transmission.

Hello, It sounds like you may have a voltage regulation problem which may be preventing the alternator from doing it’s job properly. The voltage regulator is a unit that regulates the charging of the battery by the alternator and maintaining a certain amperage while the engine runs. When the alternator is not working properly, this may result in the battery quickly losing charge and the car losing all power as you have described. You may also notice a whining sound as a result of the bearings inside the alternator begin to fail. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your charging system.

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