09 Prius Randomly total loss of memory and restart when turn off car

What leads to this conclusion? I'm thinking: drives rough, bad fuel economy, clock reset, radio presets gone, phonebook wiped, etc.

At any rate, the traction battery and inverter would have no effect on anything like that. But a loose connection on the 12v might do some weird things. If you tell us what you observe, it would be helpful.

 

Everything about this screams 12v battery or 12v battery connections..........

 

be sure to check negative connection to body

 

A healthy 12 volt battery in this car lives at around 12.6 volts.

When testing 12 volt battery condition always use the front jump point. It does not matter what it measures at the battery only matters what’s hitting the front fuse box.

If your battery is over 5 years old and has been sitting a lot from covid
Just replace it. In the reinstallation you may discover the loose connections.
Plus you can clean all the water out of the battery hole.

 

thanks! i hope that is it.

 

Nope, that was ruled out when you said this:

So your issue only happens at times when the traction battery is out of the picture.

 

You could test it, or have it tested. It's a little more advanced than just a voltage test; not sure of the best term to search would be, maybe electronic automotive load tester. I use a Solar BA5, current model is BA9. Ancel comes up a lot, on Amazon. A lot of automotive retailers selling batteries will have a pro-level tester, and be willing to test for free.

 

Unless you actually test it, you're just assuming that's not it; you don't know it. New batteries have been known to not be charged up or even be defective. But by now, unless it's defective, normal driving should have brought it up to a normal charge. But I'd still check it if it was mine.