My '08 Prius is having some weird electrical problems. Is this a bad battery, or something more?

Some of you might recall my previous post a couple months ago, wherein I detailed a crash and the subsequent repairs to my 2008 Prius Touring Edition. I got the car out of the shop a few weeks ago (she spent more than a month being rebuilt), and for the most part she's been as good (or better!) than when I bought her in Feb. of this year. After all the repairs, she runs great, looks like new, and even gets slightly better MPG than before (probably due to the oil change I had done while they had her in the shop).

However, for the past 3 days she's been acting really weird in some specific ways (listed in no particular order):

• A few times when I've parked and tried to power the car off by hitting the Power button, rather than just turning off, she has gone into that partially-booted mode you get when you hit Power while the car is off *without* pressing the brake pedal. When this happens, I've had to putz around with the brake, Power, and open/close the drivers-side door before she would fully power on and then (when I hit the Power button again) power off. Weird.
• Starting yesterday (or maybe once the day before), when I try to power up from being completely shut down, nothing happens. Nada, zip, zilch. As above, I end up putzing with the key-fob, putting it into the dash socket, removing it, opening the drivers door, etc. Eventually (and apparently randomly) it will just power on like normal and drive like normal
• This morning I walked up to the car to leave for work, and the doors wouldn't unlock. I ended up using the physical key from within the fob to open the door, and spent ~10 minutes poking around with the Power button and the little button near my knee that allows / disallows the keyless-start feature. On one unlucky attempt to get the car to power up, the anti-theft alarm went off - I'm sure my neighbors loved that at 5:10am. Eventually she powered up just fine and I got to work with no trouble
• However... once I arrived at work this morning and powered her down, she immediately lost all power, and is currently sitting in the parking lot with all the doors unlocked (because I can't lock them from the outside)
• Finally, and I have no idea if this is related: the little "bump" within the drivers-side power window rocker (the thing that rolls the window all the way up or down without holding the rocker) suddenly stopped working late yesterday. When the car is powered on, I can roll the window up or down, but I have to hold the rocker - pressing it to active the auto-roll feature does nothing

While I was sitting in the parking lot this morning, I looked up the trick for accessing the Diags menu, which report my battery with 13.9 volts... which seems a bit odd for a 12-volt battery. None of the other symptoms I've read about seem to apply - no random beeping, my lights are nice and bright, etc.

Sorry for the long post - I figured an info-dump of everything I've observed might help!

Thanks for any suggestions.

TL;DR: 2008 Prius acting weird, suddenly has no electrical power when the motors aren't powered on. Wth?

 

and thanks for the helpful and detailed checklist! My first attempt to perform the test you suggested accomplished nothing, as the car was playing paperweight and refusing to do anything at all. I turned into a contortionist, pulled all the stuff from the back, lifted the floorboard and tray, got the rear hatch open, and jiggled all the wires going into / out of the battery. After doing this, suddenly I had power again, so I tried your test and got the following results:

First test: 12.1 volts
Second test (after hitting the Power button): 11.9 volts

Those numbers are well within the normal range, right?

I did notice that the connection to the "positive" terminal isn't rock-solid - the battery cable is fairly loose and can wiggle around a bit, though it's fully seated around the post. Now I'm wondering if this is just a case of minor corrosion on the battery terminals causing a poor connection...

Any further thoughts? I'm thiiiiis close to dropping $200 (that I can't really afford) on a new battery...

 

Thanks everyone for the advice and feedback! I just finished cleaning the terminals and reseating the connectors - so far, so good. I'm going to take her on a drive, but I'll hold off on the replacement battery for the time being.

I freaking love this community - I've only been a Prius owner for a couple months, but I've seen more kindness and helpfulness from you all in that time than in the 10 previous years as a VW owner. Really, thank you all!