Was flying IFR in the clear on top of an overcast layer today. I noticed at
some point that the ammeter was indicating zero, and not moving. The Alt
warning light was not illuminated, except when I pressed the test button. I
started to shut down non-essential electriconics in case this was for real.
After a minute or two, the ammeter needle resumed normal indications, and
stayed that way for the rest of the flight.

Hmmm - I thought the ammeter *should* indicate zero when the battery
is fully charged and the electrical load is not changing ? What is the
"normal" indication you are refering to ?