I found this video interesting. He takes the time to explain the communication between the PCM and the Alternator and why there can be a fault in the system even though the battery light is off and the gauge shows it's charging.

'18 Highlander - AMSOIL SS 0w20 / ATF / Severe Gear
'06 Santa Fe - 535,000km AMSOIL SS 0w30 / ATF (R.I.P)