Have owned my prius for 6 years and never had a problem until now. Many warning lights, check engine, triangle with ! and tire pressure, etc and also the Hybrid System warning light. Car wouldn’t drive after starting it. Started a few hours later and made it to dealership where they put a new 12V battery in. 10 days later, same thing happened. got it to dealership and it did the same in dealership, but then later started and was “fine”, no warning lights running fine. Took it home and 6 weeks later, di it again. Had to tow it this time to dealership. Started later in the afternoon at dealership. they kept t for a few days running diagnostics but couldn’t;t find anything and now they just want me to take it home again and see what happens. I have no answers and a constant worry that it will just happen again…and then what. I’m loosing my faith in the Prius…help!
Absent any more clues I’d focus on the 12 volt battery connections and grounds and the ignition switch. You always have the option to ask that one of the shop techs use it as their daily driver. Eventually the problem will happen to them, and they’ll likely be able to figure it out. If you feel lucky, try driving the car with just a single key in the ignition, rather than a key chain. Ity can be very difficult to solve this sort of problem unless it is occurring while it is at the shop.
did you have any “new” electronics installed or replaced in the car on the time period close to when troubles showed up?
new radio? amplifier? something else?
any “YES” on these question can indicate an additional power draw discharging your batteries
symptoms you are describing can be explained by both 12V battery getting overly discharged AND by high-voltage battery in pre-failure state
the first one was replaced, the second one is quite expensive and dealer would not miss a chance for such a fat upsell
do you have any periods of time where you do not drive your car for longer than a week?
do you have short trips (like under 5 miles in one go) often?
any “YES” might hint toward your usage pattern not giving batteries enough time to charge properly
I’d post a detailed description of your problem on Prius forums, such as Priuschat. Somebody there might have had the same thing happen to them.