Andy writes:

I had a similar problem with a Hyundai Accent.
Exactly the same symptoms as low low battery OR
corroded battery terminals...
A hydrometer
said the battery was OK, a voltmeter said the battery and the
terminal connections were OK, fuses were OK, and I was stumped

UNTIL I saw some small copper bits on the driveway.......

It seems that mice or squirrels had made a little space for themselves
beside the battery and there was a wire in the way so they just chewed
it out to make more room.

Fortunately, they had left enough lead at the connector that I could
splice/solder in a jumper to repair the missing 3 inch section.

I never did find out which wire it was since once the problem was
fixed I lost interest. I THINK, however, that it went from the
positive
battery terminal to the fuse box, but I can't be sure.

So, you may have some missing wire sections.

This has happened to me in this car, my truck, and twice in
,my motorhome. Mice and/or squirrels....

Good luck.

Andy in Eureka, Texas