This is one of those intermittent issues driving mad any car driver:

What I have:

New battery, new alternator brushes, new current regulator, new belt. Polished brushes tracks. All properly installed.

Problem is: sometimes the battery gets discharged in a 20 to 40 minutes evening trip. Not completely out, but not enough to crank the starter. This new battery comes with the magic eye, green means good, black means discharged. When this happens it obviously turns to black.

The car came with an amp meter in the dashboard. In any case, it shows good readings when the engine is running. When the engine is in idle it is a bit off the 0 +, when accelerating the needle moves towards the end of the scale if I gas it enough. During driving, the amp meter always shows some + reading. I guess, the alternator is dishing some juice, right?

But even under that circumstances, sometimes the battery gets discharged. In those cases, I can see lights dim on idle, getting brighter when gassing the engine.

So...what to blame?

Car is a 1970's Fiat 126p...no electronics, no computers, no fancy stuff, carburated, alternator with external regulator, regular headlights 90/50, no stereo. Just a bareback pony :)

  • Good to see you, Aram! Interesting issue :o) Dec 12, 2017 at 2:03
  • Is there a battery drain when the ignition is off?
    – GdD
    Dec 12, 2017 at 10:25
  • A 1970 fiat should have 60/55 headlights. You should measure the demand as well as alternator output - if they are equal then there is none left to charge the battery...
    – Solar Mike
    Dec 12, 2017 at 15:51
  • Weird. You are not talking about an Electric car right, which consumes battery for its movement :D
    – BraveNinja
    Dec 12, 2017 at 21:41
  • 1
    Depending on how the ammeter is connected, it can show a 'positive' reading because there is current flowing from the battery to the lights and accesories. That is, if it is wrongly connected to the battery after the dynamo. It'll never show a negative rating then. If it's an oldskool DC generator with external regulator, it shouldn't deliver any current at idle(kicks in only after revvig it up), so the ammeter should show a negative reading at idle. If it is a more modern alternator then this is not an issue. If the regulator is connected wrong, the battery will discharge through the dynamo
    – Bart
    Dec 12, 2017 at 21:50


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