HELP! Weird battery problems--lights ON but car won't start!

Before all this started was the traction battery state of charging good? On the screen what was the charge level looking like? That might have warned you the traction battery (The big $$$) was going out on it. I'm hoping it will at least allow you to perform this: Insert the key like your going to start the car BUT DO NOT STEP ON THE BRAKE---JUST TAP THE START BUTTON TWICE. NO FOOT ON BRAKE. That puts the car into IGN mode. All dash lights and multi function screen should come on but car does NOT start. Toggle the screen to the state of charge screen and what do the charge level bars look like? And what color are the bars? This will tell you the charge level on the big battery. The expensive one. If it will not allow even the dash lights to come on in IGN your hosed. That would mean a very dead or disconnected hybrid battery. Did it throw any alerts previously on the dash...you know red exclamation points. If so it has a failure code stored that the dealer can check. If it does allow IGN to come on & the charge level of the traction battery on the screen is good like a few blue bars then you have very bad problems.Could possibly be a shorted MG motor which is essentially the starter motor issue but not sure about all the other electrical issues. Bad main harness? BTW, both MG1 & MG2 are part of the transmission or power split device. Also what is the condition of the trans fluid? When was it changed last? You didn't happen to notice a loud whining sound coming from the front of the car when you were driving did you? That sound portends a failing motor/generator (MG).
The little battery you had checked does very little. Boots up the computer really. The big battery does it all. I would check the charge bar level if you can and let the experts weigh in here tonight. I just read alot but there's peeps on here who really know there stuff with this car.Good Luck!

 

no go

On Liz' Prius model there is no start button. You really have to turn a real key.

Weak 12 volt battery, or it with intermittent connections can cause many strange things as she noticed. As the battery was just replaced (and presumed good), I suggest looking for intermittent or corroded connections.

Ed mentions sveral other matters that might turn out to be involved, but we must begin by confirming that the 12 volt is doing everything it is supposed to do.

 

I don't mean to sound too simplistic, but the terminals on that WestCo(fits Mazdas) battery are not marked well after the protective caps come off. Also, to make that Mazda-compatible battery go in a Prius correctly, the "front" of the battery has to face away from you, in other words, backwards. Maybe get a good flashlight and see if the battery's + and - connections match properly.