Hi Jeffroooo,

13.8v is a good enough voltage to charge a battery. It's at the lower end of the scale, but anywhere from 13.8-14.4 is correct. Lower voltages of 13-13.7 are also acceptable but not correct for a Bosch system. It's a bit of an old debate on 'what should the high voltage charge be'. Bosch have always said 14.4/5v but other car manufacturers say 13.8v because they think anything higher might fry sensitive electronics.

Are these new alternators you are getting or used?

There are plenty of people selling 'rebuilt' alternators around that replace the voltage regulator and that is about it. Give it a lick of fresh silver paint and that's 'fully rebuilt'. Hope you get better luck with this one.

Remember if your battery is fully charged, your alternator output will drop off. Drain your battery down a bit (engine off, lights on) and then see what your alternator puts out. If you changed your battery between tests, then that will also give you a different result.

A tired battery will place continuous strain on your alternator. Best to replace your battery when you feel it's on its way out.
Trying to get the last out of a battery is taxing on the alternator (and electric motors).

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1995 E300 Diesel