Voltage Meter Reading

Thank you Jack for your words.  Just FYI, I have an alternator not a generator and the battery is brand new.  I disconnected and reconnected the regulator and have not had a repeat of the problem since.  Also, I asked my A&P/IA to take a look at it during the annual.  Cannot replicate the issue.  So I guess (?) it's resolved.  Or at least I hope.  I'm having a new transceiver installed that I'd really like not become toast.

Due to the low current capacity (quite low) of our generators and the battery size (and age) of a fresh (good) battery, battery increases of this magnitude for only a "few seconds" should never exist. Think of the battery as a 5 gallon pail and the generator as a coffee cup working to fill that. Yes it can happen, but the voltage should be a gradual change as the battery is charged up.
I would pay attention to other things which may be occuring at the same time - like a radio or transponder transmitting, maybe a strobe light flashing - these will induce a level into your voltmeter to make it "spike" or possible pegging the instrument as the photo shows.
To see this great of voltage for long periods of time will damage your electronics. The battery (if good) will be the best "filter" for all surges that your money can buy.

I disconnected and reconnected the wires on the regulator and have not had the issue again. Must have been a loose wire. However, I did report it to my AP/IA who is doing an annual now. He's not noticed any issue.

Hmmm, you might put a charger on the battery to make sure it’s topped up. It might not have come fully charged. The chances of the new battery being defective is very small, so I’m putting my money on the voltage regulator or the wires thereto being the problem,…
I hate to say start changing things out. Do let us know your findings.

Yes, it is a sealed AGM battery so I guess technically it’s lead acid. , I have an alternator and not a generator.

So is your Odyssey battery lead/acid, or is it Lithium?
Cheers,