The way I have done it for years without fancy equipment:
The 14.2 i(or so) is alternator output with the car running. If it is lower (or possibly higher), test alternator..
Car not running will give you your battery capacity (at least 12.6) but a load test is the best diagnosis for the battery.
Without a load tester, just check the battery with a voltmeter and test it again after sitting to see if voltage drops much, it should drop slightly.
If it drops much, likely battery not holding charge. Load test or replace.
Battery life is much shorter with newer car electronics, Crossfire is a good example, 4 years or so, not like the good old days.
I learned this about 50 years ago from an old mechanic that lived next door and has come to use many times.
Happy driving all, stay safe and best wishes for the holidays.
Steve