Sloepoke writes …
It is my understanding that once a battery has been depleted it needs to be charged with a battery charger . An alternator needs a certain amount of battery voltage before it will start charging the battery back up . Older vehicles with generators would charge a battery from dead . Correct or not folks ?
I wouldn’t say that, at least from a theoretical viewpoint. An alternator is designed so that it should always be able to charge the battery, even if the battery was 100% depleted of charge. It may take some time to fully charge it is all.
From a practical viewpoint what you say is true though, as it can be difficult to impossible to start a car with a totally dead battery. If the engine won’t start there’s no way for the alternator to charge the battery. And another practical reason why you are right, it is better for the battery to recharge a totally dead battery with a battery charger, as you can limit the amount of current with the flip of a switch. Charging at a lower current is less harmful to the battery, especially when charging from a totally dead state.