Explain battery & alternator voltages please

[Mgicm]

I feel like im not fully up to speed so going to ask some basic questions on a 73 gmc with 350 engine.

1. Brand new battery reads 12.65v with truck off. When truck is running, i see 14.4v being sent to battery. Come back next morning, battery at 12.5 volts. Is this as expected? Or should battery be holding 14.4v? Or might something be draining overnight. I dont think it is draining overnight as right after i shut off it is about 12.6 and about the same the next morning but have to test more.

2. Had a few incidents where truck would not start after driving for 30+ minutes. I thought it was a hot start issue but might not be. Truck started fine, drove 30 mins and shut off. Came out 15 mins later and nothing. Sat for 3 hours and still nothing. Battery showed 12.5v. Got a jump off another car and started the truck like it was not even an issue. But it starts in the am cold with 12.5v. Totally puzzled.

Battery was brought back to store and checked to be good. no issues with that. Alternator is 2 months old and seems to be ok as i see the 14.4v when running.