Questions about the battery and charging system

Has anyone else been monitoring the battery voltage of their car while running? I'm noticing that at idle I measure only around 12.6 volts right after starting. And after cruising even 20 miles or so at highway speeds of 60 mph, I almost never see even 13 volts. After driving 40 miles today, all on the highway, it finally was showing around 13.2 volts of charging. Don't these numbers seem really low? I'm expecting to see upper 13's and above 14 some of the time, but have never seen even close to that.