It would appear that the common word of wisdom is that car alternators provide 50A of output. I actually looked at the supposed specs for my 2008 Jetta 2.5L on the internet -- a compact car -- and it would appear that it might be rated for 140A 14V (in ideal conditions?), which is a lot of power -- 1960 watts!
How much of this 140A ends up charging the 12V 61 Ah 330A DIN battery of the car?
Is there a way to determine whether the battery is getting a sufficient charge from the alternator in various operating conditions?
For example, it would appear that my alternator has passed the AutoMeter BVA-230 test at O'Reilly Auto Parts just fine, same for my 6-year-old OEM battery (which within the subsequent week has refused to start the engine after an overnight at 7°C).
However, after I pressed them for what's going on (during the above visit where everything has passed all of their tests and they were ready to leave me alone, assuring me that I have absolutely nothing to worry about), and asked for a re-test with both of the heated seats turned to the max, and same for AC, with the car at idle, they did immediately say that my alternator is failing several of their tests and I must replace it ASAP; when I explained to them that it's not supposed to power so much stuff at idle, and asked for a third re-test at higher RPM, it seems like it did again pass the voltage test now, but supposedly still failed a test called "diodes".
In manual testing with the 12V car voltmeter, it does appear that I have about 14,1V to 14,3V at idle with everything off for a few minutes after starting the car, but if I do turn both seats and the AC on, then it goes down to maybe as low as 13,1V or so.
At such 13,1V at 600 RPM idle with lots of stuff being on, is the battery still charged, left neutral, or is it actually being discharged?
Does it help to rev the engine (maybe to 2k RPM?) prior to turning the key off, if it was left idle at 0,6k RPM for more than 10 minutes, with all the accessories being on? How long should one rev it for and to how high an RPM? What's better -- revving the engine for a while, or simply turning off all accessories, and not revving?