Well, here is the thing, what you said about battery voltage when the engine is running is correct for a car without smart charging, for any car with smart charging, and the system working as intended, you will normally see only 12.6Volts maybe while driving under power, on the over run you could see something a lot higher than 14.4Volts as the charging system crams charge back into the battery on the over run and especially while braking.
Sort of regenerative braking to improve emissions.