No, because :
-Heat=less charging (volt. regulator drops it's charging cause of heat)
Yes it does this on purpose, for a good reason.
-Driving always with headlights on (by law) and fog lamps (cause I want to)
I'm annoyed by foglights when there is no fog
-It DOES work, Voltmeter isn't lying
Yes, it seems your duct does cool off the VR well, getting an about .2-.3 voltage rise?
-it will prolong alternator life cause it will take some of the massive heat produced by
alt+engine+exhaust manifold
Super agree, should make VR last longer too.
-It will prolong life of the battery cause the charging will be more stable (and I run Bosch battery so I don't wont to kill it prematurely)
Not so sure about this.
The VR intentionally drops the charging voltage as ambient temp rises, because batteries charge better and last longer with lower charging Voltage when they get hotter.
(You want the charging voltage to be lower on hotter days.)
How well the VR stuck on the back of a hot alternator next to the exhaust can do this is debateable.
I hope that Volvo and Bosch engineers worked together to plot out ambient temps versus engine loads/temps, and battery temps/charging voltage needs, to figure out what voltage the battey should get according to the VR temp.
A VR that was better able to sense actual temp of the battery would be much better. (glued to the battery would be best I think)
Modern cars use ambient temp sensors to get a better idea about the battery temperature, and change the charging voltage from the ICU.
The voltage bump you are seeing is from cooling the VR, making the alternator work harder to create a higher voltage because of the new VR input. But, you are cooling the alternator as well, making the higher voltage easier to generate. Probably zero sum, or likely less net stress on the alternator.
So, having a higher charging voltage on hot days is worse for the battery.
Cooling the Alternator and VR is nice for the alt and VR, but worse for the battery.