Back to the original point of this thread, yes you had a dead 12 V battery. I had the same exact dash lights flashing and everything. I just replaced mine with the Optima yellow top especially made for the Prius and our car (same battery). Wasn't too hard to do and so far I haven't had any issue with starting.
By the way, my car is a 2011 so that means my 12 V battery only lasted 2.5 years. That's pretty pitiful in my opinion. I did buy my car used though so I have no idea whether the original owner ran the battery down a few times. That would kill it real quick. When I pulled the battery out I put in on a battery tester (100 A load). Within a few seconds the battery went down from 12.6 V to 5 V, so ya it was dead.