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?