today, the battery sensor lit up

My recommendation would be to go to a free auto store (like auto-zone) have them check the alternator and battery voltage and fuse for the light (if there is one). If they say its good, I would think about replacing the battery sensor that lights up the "battery sensor light." Hope This Helps. Been working on and around cars with many veteran mechanics for years.

the best way to find out is to take it to an auto part store and have they run a diagnostic test on the alternator.