Battery weirdness can happen anywhere

It was a long uphill, steep enough that I had to go into my usual
just-touching-3000-RPM hillclimb mode [about 30 HP output]. After
a while it leveled off a bit and I saw another steep pitch ahead,
but could back off power for a little while until I reached it.
.
When I did, the output power ceased entirely and I drifted into
a convenient side pulloff, with the car now seeming completely
dead in the water. The dash VFD was still mostly lit, but without
the READY indicator. Almost like I had held the power button down
but for some reason left strangely a little more "powered up" than
that. There was no warning or triangle. Okay, Wth? Maybe it was
one of those Scangauge network glitches except those do usually
throw a big hairy error.
.
I went to reboot, except that now the car wouldn't READY up at all.
Just IG-ON state, and still no warnings. I flipped the panel
voltmeter over to 12V bus, and saw the needle wandering around
between about 8 and 10 volts. *Wavering*, not steady. Oops,
okay, some sort of really bizarre 12V problem but even if the 12V
battery was dead, why wasn't the DC/DC converter holding the system
up during the hillclimb?? Maybe the converter had just overheated
and eaten itself, ut-oh. Like in the teardown pictures, possibly
necessitating a new DC/DC board.
.
The sinking feeling in the pit of my guts brought me sort of half
awake, and I realized that *I* was overheated and wikkid thirsty.
Something had been trying to tell me, evidently in terms that my
"Prius pilot hindbrain" would understand, that there was a problem
with *my* electrolytes and I needed to get up and add water. Side
effect of going climbing last night and then eating some salty
chips when I got home, perhaps...
.
No really, the car's fine, not to mention completely uninvolved
in this little event. Although lately I've been noticing that
the Yellowtop I put in there 2 years ago has been giving slightly
less voltage when supplying loads in non-READY mode, so perhaps
that factoid was in the subconscious somewhere. My usual
car-related sleep imagination involves healthy paranoia about
uncontrollable situations and imminent crashes, which helps
keep me humble about what could happen on the road.
.
_H*