15V

My 68 has been running 15 volts since about 2000.... it makes for nice bright halogen headlights that I power up with relays triggered by the run circuit......... cuz up here it's the law. Well it is for cars that have DRLs; but I figure it's best not to give the cops a right-now reason to pull me over.
One time, it was up to 18 volts at idle with a "stuck" Electronic regulator. I was many miles from home. I just unplugged it, and replugged it, as needed, until I got home; then swapped in a different used one. I had several of them and I liked the 15volter, so that's what she got.(I think it's actually a tic over 15, but no biggie to me). I've seen lotsa Chevys run higher than that. Rule of thumb to me is she's gotta run 1.25, +/- .25v over battery rest voltage. I run a dry-cell technology Optima with a rest-voltage of about 13.2-13.5, so by my rule, she's on the high-side, but the Optima has no fluid in it to boil away........... so it's all good.
BTW, that Optima was ~14 years old before it could no longer hold it's charge over winter, parked outside, in the minus 35C temps. But it still works today, now ~18 years old. Expensive buy-in, but in the long-run; the cheapest darn battery I ever bought. Jus saying.
I know what the books say, but....... youknow .........there's books, and then there's real-world experience.If you have a vented lead-acid battery, that you never service; I guess long-term,the book-spec is best.

Oh yeah about that bulkhead connector; while my car was in the bodyshop, I, as most of you, had a year or more of time to kill, so one of the things I did was go thru my 30 year old wiring, including taking apart the bulkhead connector and meticulously cleaning it and "restoring" it. The car had not been driven since before 77, so it wasn't aged in that respect; I just wanted to be able to claim victory over it.
Well that lasted about a year,and then every time I turned the headlamps on, I would catch a whiff of hot plastic. Thinking the switch was the issue, I just turned them off. Shortly after, I was again about an hour from home and the hot plastic smell came up... with the headlights now off... Well, I had to do something fast. I'm a mechanic so I always have tools and an emergency kit on board, and a short time later we were moving again.
After I got home, I installed heavy-gauge jumpers thru the bulkhead, soldered,shrink-wrapped,and taped, and that was about year 2000. And, I never smelled melting plastic ever again. I highly recommend this remedy to all similarly equipped cars. For you guys that are averse to drilling your connector, think about this; if you smell hot plastic, chances are the ammeter wire is already drilling it's own hole thru there, and if it finds a ground, well, it's a 10 ga wire......... try hooking one across your battery posts and see what happens....