Your call from the caller from Brattleboro today raised a common and pesky question for Prius owners. The death of the small battery in the trunk.
First question for Brattleboro: do her lights stay on after she shuts off the car? Ours do, and only go off when we get out. But that wasn’t our problem.
Ours failed on vacation in the Rockies. We got a jump from a local mechanic, who did a deep charge. It worked until we got home. I took it to the Toyota garage and they did a test, said it was ok. We developed a shut-down, walk-around procedure to make sure nothing was on. We always locked it to make sure no door was open, leaving on a dome light. Nothing mattered. It failed again. We took it back. They tested it again and said it was ok. It failed again. I took it to a high-end import shop, and it actually failed in the shop.
They installed a new battery (with our permission) and it’s been fine ever since.
Our car was off warranty, so the dealer shop cannot be accused of ducking any warranty claim.