147,000 Trouble-Free Miles

I walked out of work on a Friday afternoon, got into my 2012 Prius C and there was no sign of life. It's a keyless edition, and the car didn't respond to anything. I had replaced the keyless battery a couple of months ago, so I am reasonably sure that wasn't it.
My next thought was jumper cables, so I got someone from work who had cables--another Prius C owner, it turns out--and got them hooked up. My car immediately started, before she even started hers. I disconnected the cables, thanked her, reassembled her battery cover, and headed homeward.
I did have the air conditioning on for my half-hour commute--this is, after all, June in Texas--and when I got home, I tried re-starting. It was close to dead.
One other clue: I'm someone who makes a sandwich for lunch and eats at my desk, but in the past 2 weeks have, most afternoons, gone out and tried to get 15 or 20 minutes' worth of shuteye, or at least relaxation, during which the air conditioner is cranked.
For those of you who are problem solving inclined: care to speculate? I thank you in advance!

 

Thanks. I finally just jump-started it and took it to the local Prius dealer. They've replaced the battery and I'm about to go pick it up.

 

I've never had battery problems with a Prius before, and I understand that there are two different types of batteries in the Prius--that which starts the car, and those that supplement the gas engine. I was trying to access the well of experience here for areas with with which I have no experience in Hybrid cars.

 

I had to jump it twice, so yes. Turns out, my workmate with the jumper cables had a Prius C, so I had two back seat compartments to take apart and put together.