12v battery failure

Plugged my 2019 in and set the charge level to 70%. Came back 3 months later to a dead car. Would not start. Couldn't even get an interior light to turn on. Assuming the 12v battery was dead I charged it and after awhile it rose from 3v to 13.5 volts. Took it for a ride, and shut it off upon...

I've been stranded by my Bolt four times now. I come back to my car and it is completely dead. I know it's the 12 volt battery. It is not being trickle charged by the big battery as it is supposed to be. My main battery is always fully charged when I leave and I rarely run it down more than...