PWM alternators fool the tests.
I have a theory that these PWM regulators fool the normal testing procedures. I expect your independent used a carbon pile tester across the battery posts and all showed OK.
I had a battery shop do the same thing and with mine, all showed OK. What was OK was the battery. As best I can tell, the alternator was putting out somewhat but not what it should have however something fooled the procedure. Also the headlights etc worked well so quite a bit of electricity was still being generated.
Ultimately I ended up installing a new alternator as it seemed like a good idea. It was - then later a new starter motor as well - now the insta key start feature works as it did when new. (That is the feature where you just turn the key and then let go immediately prior to engine start and the start sequence proceeds automatically).
I think the test procedure may be compromised by the fact the alternator feed goes to the starter motor first and then the starter motor feed heads to the battery. This is not common. Most vehicles have a small gauge wire directly from the alternator to the battery and a heavy one from the starter motor to the battery with a third wire off the battery going to the fuse box.
Yes, I know this should not matter and I presume it does not when all is working well. The problem is when things are less than perfect.
About the only clue you get to there being an alternator problem is that the running voltage seems less than it should be. By less I mean 13.0 volts; 13.5 to 14.5 is more normal and is what is required to properly charge the battery. 13.0 will give you some battery charge and keep the lights bright but is just not enough to charge the battery - but it looks that way and there is the problem.
Do not be afraid of 14.9 VDC as that is normal when the battery is down and the weather cold. Hot weather yields lower charge voltages than in cold, as in around or below freezing when you can see the 14.9 to 15.2 measured at the OBD port. In summer, at say 80F, 13.5 might be normal and 13.9 at 60F. Also I think the screen voltages displayed on the NAV are maybe 0.2 low as I think they are what the unit sees - buss voltage so to speak rather than volts off the alternator or near the + post of the battery; in fact that is part of the difficulty - there are so many slightly different voltages depending upon where you measure.
