Most newer cars and trucks will have an alternator indicator light that will come on if something is wrong with either the batter or alternator.
The computer in the vehicle will get the information that the alternator is not working properly and should turn the indicator light on.
If not then your charging gauge will read too low when the alternator is not putting out enough power or any power at all to keep the engine running properly or to recharge the battery.
If you have a good battery and your battery always goes dead after driving the vehicle then your alternator is likely at fault and needs replaced.
The alternator may also make some bad bearing noises and your headlights may flicker as well when the alternator is bad.
A bad alternator diode can also cause a cars battery to go dead overnight or after sitting for some time.
You can have the alternator tested at an auto shop or at places such as Autozone and other parts stores and you can also have your battery load tested as well.