From my experience you will never work it out!! 
I had a VW Golf with start stop and a Mazda 2 with start stop. Both always worked perfectly whether short journeys or not.
My current Volvo V60 with start stop is dependant on, temperature and whether the battery is any good or not.
12000 miles 2 years old and diagnosed today the battery is dead even though it starts the engine every time! EFB and not AGM.
I believe the ND is too?
Lets put it this way, if I ever have to buy a new one it will be AGM.
Have a read of this thread about CTEK chargers.