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Recently, on a longer trip, the battery light came on while I was driving, indicating the alternator was no longer charging the battery. The shop diagnosed a bad alternator and replaced it, which fixed the issue. The car had some 260,000 km on the clock at the time.

I had hardwired a battery charger, to which I hooked up the car almost constantly when not in use for the last winter (and the winter before) – this mostly due to previous experience with my previous car (same make, model and year), where the battery would go flat after a few days of sitting outside in cold, damp climate conditions.

The alternator in my old car lasted for over 360,000 km, until the car was lost in an accident. Now I am wondering if there’s a chance the external charger damaged the regulator or other electronics, or accelerated its wear. Could that be the case?

The car is a 2005 Audi A4 2.0 TFSI, if it matters.

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  • "the battery would go flat after a few days of sitting outside in cold, damp climate conditions." By "going flat" I assume you mean the battery is too weak to start the car. I'd say this indicates there is a constant excessive draw on the battery at all times and when it's warm the battery can still manage to start the car. Alternators aren't designed to put out max amps for long periods of time. optimabatteries.com/experience/blog/…
    – Arthur Kalliokoski
    May 27 at 14:35
  • @ArthurKalliokoski Could well be the case, or maybe the moisture contributed to the excessive draw, but I never bothered tracking this down further. Maybe they found out at the junk yard when they dismantled the car...
    – user149408
    May 27 at 15:20

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It's very unlikely your charger had anything to do with your alternator failure, unless you were running the charger and your engine at the same time, even then I'd expect a charger to cut out as it would detect that the battery is at capacity. If you were charging the battery when the car wasn't running the alternator wasn't engaged, current isn't going to somehow get into it and mess it up. If anything keeping your battery charged would give your alternator less work to do. A malfunctioning charger can damage a battery through overcharging, but that's a separate issue.

The cause of your alternator failure is almost certainly ordinary wear and tear, probably bearing wear. 260,000km isn't bad for an alternator at all, 360,000km is kind of extraordinary, so if anything you've done well.

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  • Depending on the charger, it can fry the charger when you start your engine. I'd highly agree with your assessment that the charger would have nothing to do with frying the alternator.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 26 at 16:04

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