I bought a used 2010 Prius a couple months ago. My wife was driving it, when she saw a message on the screen saying something about the Hybrid battery, according to her. Message disappeared in a few seconds, so I do not know what it was exactly. Next day, she could not start the car. And all its electrical circuits were dead, lights and doorlocks did not work. So, I concluded that the problem was with the aux battery. I measured its voltage. It was about 1V when connected, and about 8V when disconnected. I bought a new battery at Autozone, which they recommended Duralast Platinum AGM Battery 46B24R-AGM I installed it, but could not start the car. Voltage was 2V when connected, and about 13 when disconnected. I jump started the Prius, drove it for 30 min, and left it parked in ready mode overnight, for 8 hrs total in ready mode. Voltage was increasing while it was charging. I was surprised to see 40V, but I do not know what it should be while it is charging from the Hybrid battery. After 8 hrs of charging, I pressed the power button to turn it off, and immediately tried starting it. The car does not start again, its lights and locks are not working, as if the battery is dead. Voltage is about 14V, which should be enough to start it. I checked the fuses related to power, all of them are good. Could this indicate an issue with wiring or something? Or is this battery not suitable? I have no idea where to look next.