Battery voltage has little to nothing to do with how the battery is working, you need to apply a current draw to find out if it will fail. 12.3 off is fine and 14.6 running looks ok as well but check it when you turn it over or when you turn stuff on and see what happens.

3 years is long enough, it could be bad.

no worries, your post means that mine is not that much off!!! :)

measuring the battery with a voltmeter is not the same as measuring the electrical system through the internal circuitry using the designated methods... I am not sure about the E70, but in older E53 one of the cluster tests shows the battery voltage as the car sees it, which can be different from the reading taken directly from the battery...

a 3 year old battery, even from a dealer can be already dying... and the alternator may have a bad or dying diode inside the regulator, which can be shunt, and once warmed up, would open... besides, the current draw, as mentioned earlier, can be different under different circumstances - there could be processes in the car that are running on the background...

battery should be around 12 V when nothing is connected (so, 12.3V is good), and the alternator should spit out at least 13-13.5 V in order to properly charge the battery with sufficient current - if the battery is 12V and the alternator is producing 12.5V, the charging current could be too low to properly charge the battery... so, the alt output should be over 13V (closer to 14V) to charge the battery, and not too high, as 16V will fry the electronics...

well... in other words, keep a close eye to the charging circuitry, and if the car under warranty, have them deal with it, otherwise, start with monitoring the alt, and replacing the battery...