Battery state of "health" can only be checked with an appropriate tester, which are quite expensive. Your DVOM/DMM will only show static voltage, which will vary greatly based on current battery usage. The charging system uses a strategy called "Smart Charge", which Ford has employed for 15 or so years. The charging system is controlled by the PCM, which determines charging strategy based off of current load conditions. This means that the battery will charge under low load conditions (deceleration, coasting, etc) and reduce charging load under higher load conditions (acceleration, pulling hills, etc). This maximizes efficiency and minimizes battery fatigue from over charging. The only time you need to be concerned with the charging voltage is if the battery light or a charging system fault message appears; otherwise it's operating as designed.