Inconsistent loss of power? HELP!

I am pretty new to owning a hybrid vehicle and extremely new to posting on this site so I apologize if I don't do something correctly, but I will try to make this as painless as possible to read.

I own a 2008 Prius with 146,000 miles that I bought from a private owner almost a year ago. I have had no issues with it until a couple weeks ago.

2 weeks ago I was driving my car around a short distance (it had been parked in a shaded parking garage for the entire day) and once I parked the car I pressed the power button to shut it off. It didn't seem to do anything so I pressed it several more times until the car finally powered off. After it powered off, the battery appeared to die (no lights would come on, locking mechanisms wouldn't work and car would not start).

Once it was jump started, it would run normally. I took it to O'reilly to get the battery tested since I bought the 12v battery from them less than a year ago. When I got to O'reillys the car died again after powering it off. I attempted to start the car a couple more times. While trying to gain access to the 12v battery in the trunk I pressed the unlocking button on the trunk door and the car powered up by itself. After this occurred I decided to drive it to the Toyota dealership to get it checked out.

The next day I pay $118 for diagnostics at Toyota and they find a piece of cloth in the trunk latch that they believe was preventing the trunk door from shutting all the way and draining the battery (however, the open door light was never on my dashboard).

For the next 6 days the car runs perfectly fine. No issues. Until 6 days later when I go to leave for work around 5:45am and the car is dead (can only unlock with the physical key part of the key fob, no lights, won't start). I make a follow up appt with Toyota for after work and plan on getting it towed there. Once I get home from work the car is working like normal (will unlock using the key fob, lights turning on, car will start). I did not jump start or do anything to it. It appears to have gained power back all by itself.

I drive it back to the dealership and they take a look at it. Later they call me and say they are unable to duplicate the concern and it is running fine for them. They said all battery terminals look good, the battery is testing normally and they are unable to do more diagnostics unless it is brought in "dead".

I pick it up and the next morning I get in to drive it (working normally so far, haven't started the car, but lights and locking mechanisms are working) until my boyfriend gets in the passenger side and it immediately dies. Almost like the slightest movement makes it lose power from the battery?

So today I had it towed back to the dealership for them to look at tomorrow. The tow truck had to use cables for it to power on so we could get it in neutral, but as soon as I powered the car off it went back to its dead state.

To make it clear.. the car NEVER dies while I am driving. Just when I power the car off all the dashboard lights disappear, headlights won't turn on, interior lights don't turn on, locking mechanisms don't work.

I am very unfamiliar with this car and how it works so any advice would help. My first thoughts are maybe an electrical issue with a wire or cable connecting to the battery? Thanks in advance!

 

Hi everyone! Thank you for taking the time to reply. Toyota informed me last night that they have narrowed it down to being a bad battery after all. It would test normal when sitting in the car but if it was taken out and tilted the slightest it would read as drained.