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Battery voltage 12.4V at rest with engine off

Battery is only 2 months old, but at rest it was about 12.4V and today it was 12V (I think this means about 50% charged?). I turn the engine on for about 20 seconds and turn it off, and it will then be about 12.6V. Alternator output voltage is about 13.5V, and rarely it will be abut 13.8V, and mechanic who put on the alternator was adamant there is zero problem with the alternator. Is 12.4V on a new battery ok? I have two small dash cams plugged in all the time, so they would be parasitic volatage consumers, but they shouldn’t discharge the battery that much in my opinion. Please give me your thoughts.

Seems pretty normal to me but I wouldn’t like the cameras plugged in all the time. You can’t tell the state of charge of a battery by checking the voltage. Even a battery that has lost most of its capacity can have a decent voltage reading. You want to look at cold cranking amps available.

I agree that those readings seem pretty normal.
As to the dash cams, if the power outlets into which they are plugged are “hot” even if the ignition is turned off, I would suggest unplugging them. My power outlets are shut-off when the ignition is off, but yours may–or may not–be the same.

you don’t have a problem. Enjoy the car. I would unplug the cameras unless you drive the car frequently.