weird electrical issues with my 2012 Prius 3

A week ago, I closed the door to my 2012 Prius 3 when the key was inside, and the doors locked. The engine was not on, and I don't recall whether I locked the doors or not. However, I thought the doors are not supposed to lock if the key in inside. [The police had to pry open the door]

Then the next time I went out to the car, which is in the garage of my apt building, my Prius' lights started flashing when I exited the elevator into the parking garage. I had not touched the key in my purse, and this has never happened before. I then approached the car, and the dashboard was illuminated! I certainly had not left the car on. The doors would not unlock despite that I had the key in my purse (as they normally do). I took out the key and pressed the button to unlock the doors, and this time, the doors unlocked, and the dashboard went back to normal (i.e. nothing illuminated).

any thoughts on what this could be? thanks!

 

I replaced the battery in the key fob about 5 weeks ago. I'm not sure how old the 12V battery is...

Any suggestions on how I can test the battery?

thanks for your help!