I'm currently trying to figure out what is wrong with the car, but I'm not sure if a rogue drain somewhere is able to give such symptoms or did the battery just die.

The voltage of battery stays at an okay ~12,8V when the car is turned off, but turning the ignition on makes it drop to the values as low as 8-9V very fast, like within 30 seconds. The car, miraculously, can start after a couple of tries, and then the voltage goes up to 14V+, so I guess at least the alternator is charging fine. The car is a '00 Mazda Miata, no AC, no alarm, just aftermarket radio and amplifier that has been working fine for the last 6 years (but well, there's always the time something goes rogue)

The question is - would some strange drain be able to bring the voltage so low or did the battery simply decide to die?

  • 2
    Its either a bad battery or the charging system is not working properly. How old is the battery?
    – Moab
    Aug 22 '19 at 21:45
  • Seems like it's the battery - mounted a different one and all voltages - charging, idle, turned off etc. are at proper levels. The battery is only like 3-4 years old but has been deeply discharged a couple of times during car restoration by sitting for months inside the car without charging, which probably wasn't very good for it's health...
    – Rachey
    Aug 23 '19 at 15:23

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