If you are unsure, you can LOAD (not just volt) test the battery.
It is easy to do, any part store or Wally with service center can do it.
They may try to charge it first, though so you have to wait or leave it there if the charge is low.
But judging from your description, I agree with anybody here that the battery is bad.
The battery needs to be replaced.
Unless the alternator is bad but you cannot really test the alternator until you put a good chargeable battery.
Then you can run the engine with AC, radio, etc. on and see if the alternator can keep up with the load tester on the battery.
It is easy to do, any part store or Wally with service center can do it.
They may try to charge it first, though so you have to wait or leave it there if the charge is low.
But judging from your description, I agree with anybody here that the battery is bad.
The battery needs to be replaced.
Unless the alternator is bad but you cannot really test the alternator until you put a good chargeable battery.
Then you can run the engine with AC, radio, etc. on and see if the alternator can keep up with the load tester on the battery.