My mechanic said, that an alternator on my Mercedes B200 (W245, diesel, 2008, 1993 cc) needs to be replaced (because of red battery sign, that is shown and beeps from time to time). My original alternator reference number is A6401540502. I've bought Valeo 439552 because of a good price and apparently it should match my car.

However, my mechanic said, that although it fits in other respects, the new alternator doesn't have voltage regulation and always output 14V. Hence he cannot install it on my car, because the battery can explode.

So my questions:

  • Can battery actually explode if charging constantly at 14V? (Or shorten the lifecycle?)
  • Maybe an additional voltage regulator is needed? Or I can install the new alternator without regulator?


1 Answer 1


Q1 yes, it could explode as the gases given off are flammable / it will shorten the lifecycle.

Q2 no, you can't use the alternator without a regulator - most likely that alternator requires an external regulator - simple solution get the regulator and fit it to the alternator.

The other option is to take back the wrong alternator for a refund and get the correct one...

  • What the choise of regulator depends on? Apart from alternator itself.
    – stop-cran
    Oct 18, 2017 at 12:02
  • 1
    The regulator that matches that alternator - if you want to try to use a different regulator then you will need a very competent vehicle electrician to be able to make the appropriate connections / adjustments...
    – Solar Mike
    Oct 18, 2017 at 12:07

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