Prius with 193K miles and repeatedly dying 12V: repair or donate?

All seems well -- looks like a fix! Checks by multimeter on the neg terminal of the battery confirm that there's no undue parasitic draw. And I've put a multimeter in the glove compartment and have been monitoring the health of the battery after every drive. While I was repairing the car, the battery's charge drifted down to about 12.8 after days of non-use, but my wife drove the Prius on the long route to and from work today, and when she returned the battery read something like 13.19. Looks like it's charging as it should. I turned keyless entry on a couple of days ago and have replaced the battery in one of the key fobs (the second fob appears to be water damaged and I'm going to have a go at reprogramming a factory new fob via the "chicken dance.")

My able assistant Sam extends his thanks to the group for bringing his Prius back from the brink (he's repairing our 1993 Camry here, but I'm quite sure his inspiration was all of the work we did together on the Prius):

 

I'm guessing the problem was either the loose positive cable, or the fairly heavy corrosion on the negative terminal and cable. Hard to say for sure: I sanded and cleaned everything down quite exhaustively, so it may have been a combination of things.

We have also noted a propensity by my able assistant to turn various lights on, prop open various doors, and depress various buttons inside the car. We now have a protocol where we check all doors and lights before we retire for the night. This evening, I noticed young Sam propped open my Camry's door, and turned on two lights in the Prius...

With that in mind, I'll surely heed your warnings about hammering on various car parts. Here's a few more pictures of Sam hard at work. The awesome part was the absolute certainty with which he effected his repairs: he would pick out a certain part, put it in place, and hammer or adjust for long minutes until he was satisfied the job was truly done. He worked diligently for at least fifteen minutes. Indeed at one point Sam insisted that I go back inside the house to retrieve his toy screwdriver. Essential!

 

Wanted to offer a happy update to this long-lost thread. The Prius in question has run without flaw for another 11,000 miles since the group collectively fixed it last summer, and has not required any other repairs. We've moved to SoCal in the intervening time and the car made the 400 mile journey without complaint. Bought a mini VCI cable around the time we did the other repairs, but I haven't had cause to use it. The car is now approaching 205k miles: any bets on what the next part I'll be fixing might be?

Thanks again to everyone for the help diagnosing this, it's nice to have a "free" prius for kicking around SoCal.