I noticed this off an on last year, on my 2012. It would drop down around 10, idiot lights lit on dash, and within 5 miles it would pop back up to 14. Twice it went to 16 for almost a mile, then back to normal. Over the winter, I had the bike torn down for some repairs, and put a new 600CCA battery in the bike. Second ride this year, voltage drops to 12 and stays there. By the time I got home, bike was at 10.5 VDC. Pulled the voltage regulator, tested the stator to be operational, and ordered the Cycle Electric voltage regulator. Once installed, fired the bike up to an instant 14.4 VDC. Two more rides with NO fluctuation. Harley's regulators are not the best design, and the Cycle Electric regulator mounts up higher on the front frame tubes to get it away from the heat of the oil cooler. My $.02.
2012 FLTRX Chrome Yellow, Rinehart True Duals, SEPST, Big Sucker AC, 19" / 18" chrome Agitators, chrome lower legs, Alpine UTE-62BT, JM Rokkers