Brand new 12v battery-car won’t start...help!?

here the deal with my 2006 Prius. I was driving normally but started to notice a loss of power sometimes from a stop to get up and go again. It would do it, but seemed to hesitate. Then, after about two weeks of this my dash lit up. Red triangle. Check engine. The one for the brakes. The works. I immediately drove home and parked. Over a couple of days I did the self check on the 12v from inside the car which read at lower end levels, but would still turn the car on, power windows, lock/unlock, etc. the car would still drive, even but I was scared to. So. Replaced the 12v battery with a brand new one. Cleared all the lights, seemingly just from having the battery disconnected in the replacement. Drove around a bit and everything was GREAT. stopped to get gas, left the parking lot and there is a speed bump. When I went over the bump (not super fast or anything) the lights all turned back on. I returned home. I did some searching and decided I needed to check my oil levels as I’m just over 200k miles. All seems well there and with recent oil change. Also, the hybrid battery was replaced at 171k miles for some background. Two days later, we attempt to start the car and get nothing. The brand new 12v is dead. We jump it and all seems well but why is the 12v dead? So we decide to try to trouble shoot. Trickle charge the 12v overnight with 2amps and it’s reading on a voltmeter as a full charge. Reinstall that into the car. At this time we also followed directions for the (I’m blanking on the name) but the orange tab thing on the side of the hybrid battery which apparently can be knocked loose but can be reset by removing and then reinserting correctly while in the process of 12v battery change. So we did that also as a precaution. Went to start the car....mind you 30 minutes ago the 12v read at a full charge. Nothing. Crickets. The most I could get was the door open light. Then after trying to start the car, even that wouldn’t come on. Check the battery again. Nothing. It’s reading at around 2volts!? Jump start it with another car, finally get it started. First, no warning lights, then remove the jump cables and thinking about driving around our street to see what happens. As soon as it’s is put into reverse, lights up again. So we pull up the on screen battery check screen by way of holding display and turning head lights on and off. When the car is running (from a jump start) the battery shows 14v. All numbers look great. But if you shut the car off and try to restart, it will not start without a jump. No power at all. Can’t control windows or locks. Dead. Just reread the 12v battery while it’s off and we are reading 5volts on it right now.
I’m dumbfounded, stressed, and clueless at this point.
Can anyone please point me anywhere?

 

Also, after much reading...there is turbulence in the coolant resevoir which I read could indicate a bad inverter if there was not. Car doesn’t show any recalls. I continue to find suggestions and everything checks out as fine so I cannot understand why I have all these warning lights, a dead brand new 12v once connected. Just looking to be pointed in ANY direction.

 

The battery was replaced by a Toyota dealership before the car came into my possession. Nothing plugged in at all that should be drawing power. And the thing was, the battery was fully charged reading great, but then dropped to almost nothing after installing and attempting to start....wondering if this battery is a dud? Obviously it is under warranty, so that’s not a huge deal to swap and see if that helps my issue, but I don’t really want to be blowing through batteries if any of these things are indicating a different issue.
We ordered a reader that is compatible with the hybrid system and can be linked to a laptop so we can get as much info as possible from that...but it won’t be in until Tuesday, so waiting there because standard OBD II has not been informative. Glad to hear we went the right direction on that.

 

This is certainly something we have looked for as mice DID get into my boyfriends car last year! We are seeing absolutely no signs of that and actually it looks pretty clean. Visually, seems like nothing should be wrong anywhere and it’s actualy really clean.

 

I purchased the car from a family friend when she got a new car and didn’t need it and i was in desperate need of a car at the time, so no, a dealership didn’t sell a car that high in miles. I was around when the replacement battery occurred, so while the paperwork is lost someplace, I do know it was done by the dealership.