Parked in the garage, Thursday tried to start Saturday, nada. no lights, nothing. Put Stanley charger on no action from any button, charge, recon, etc. Disconnected the car cables and reconnected the charger, and left it. A few hours later, Recon self-started. What's going on? Could there be a short in the car wiring? How would I find it?

 

How old is the battery? Could just be junk and froze from sitting.
Does it make a big spark when you hook the cables up? A tiny spark is normal, but nothing huge.

To test parasitic drain you need to put a multimeter or clamp meter inline with the positive cable, and pull fuses until the current drops back to normal, then trace whatever circuit that fuse protected until you find the fault.

 

Basics first...Have your battery AND your charging system tested. That will almost assuredly give you the data you need to make the best decision on the fix...

 

There could be a few things going on.

Unhook your battery and charge it up with a 10A charger. Get a simple toaster-style battery LOAD tester, from like H/F ...test it. That'll tell you a lot. If battery is good, then look at cables, wiring at the starter ....or the starter solenoid. Those are likely the culprit. Could also be the switch.

 

Also wiggle the shifter as you turn the key, in case the Park-Neutral switch is not making contact. That could cause a no-start and suddenly-start situation. Maybe the battery was never low/dead and the N-P switch just happened to work the 2nd time. I've had that happen before, several times.

 

I'd say test battery first since you said no lights no nothing then go from there if you get batter tested and it's good check for a parasitic draw killing battery over time. My wife's 2015 200 would die about every 3 days and battery tested good found it had a parasitic draw killing it and issue was a usb cable she had plugged into the port inside center console and cable was wedged so bad it was shorting out. My XJ had one and turned out to be overhead console light on drivers side...these things are fun to troubleshoot!

 

The success you had by disconnecting and reconnecting the cables on the battery is a big clue. You could have had a corroded connection at the terminals. That would explaining no start, no lights, and also that a jump did not change that. Clean the battery terminals, the cable ends, and be sure you don;t have corrosion inside the insulation around the battery cables - a known weak point.

 

Clean the battery posts and the clamps. oft they get a bit corroded and that can cause battery to not charge, nor provide current to run things. happened on my jeep. easy peasy to do, use a stiff wire brush to clean the posts and clamps. the contact areas should be shiny silver color.

 

If you live in Maine, you definitely need PM on your battery

 

EDIT: My bad - deleted my mistaken assumption with my apologies.

EDIT: I stand corrected @geoakley thanks for coming back and sharing the solution - well done! Hope it holds.
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Lots of good suggestions. Things take me a bit longer due to my physical condition. But after checking cables, connections, I went and replaced the 4-month-old Duralast Battery, no charge, under warranty. Damn, those things are heavy and awkward. So far so good.

 

I would also redo your engine grounds and run a new B+ to starter cable wire.