the "problem" is short, stops and not getting the battery enough time to recharge. the nissan charging system is designed with emissions in mind - meaning the system keeps the charge current low /minimal just enough to meet the demands of what the system is asking, and nothing more.
at a cold startup, you see the battery meter spike to 14+ volts, then after 30-45 seconds ish it goes back down to 13 volts. that is the design of the system. at times, the volts will go up a couple volts (you turn on the headlamps, you turn on the AC, some sensor needs more current).
so with this low charge current, the battery wont ever be charged back to 14 volts, unless you drive for some hours.
that weird looking block thing on the negative battery cable at the battery post? thats the sensor that senses how much current is being used by the car and it alerts the ECM that in turn increases voltage demand. some cats have removed this sensor, and when doing so, the alternator charges /send voltage at a much higher rate.
you car is likely fine, but i totally understand your dilemma! i bought a second battery to swap out with and keep one charged.
i recommend you invest in this little guy:
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you can use this to keep track of your battery at rest and also see the charge state dynamically. i had this on my Qx...