2013 Altima battery mystery issue (mystery to me at least)

New here, first post, hello all

2013 Altima 2.5 SL,100k miles, 100% stock

Background info: I have very basic knowledge of cars, owned this Altima for about a year, had 80k miles at purchase (assumed mostly highway miles, car was registered twice in Connecticut but I bought it in nyc), runs amazing imo and I drive it very aggressively, good car fax and regular maintenance.

Here’s the problem:
My cars battery is constantly dying or draining:
1) Engine off, playing music at a low volume for 10 minutes and car won’t start.
2) got a flat, had the hazard lights on and engine off for 10-15 minutes, the car didn’t start.
3) I parked, turned off the car, went to the atm, came back and the car won’t start

1) mechanic told me the battery wasn’t charged enough and told me to drive for a long time. I did and everything was fine
2) happened 6 months later after event 1, different mechanics had no answer but said alternator and battery are good.
3) happened two weeks ago. My grandpa said my battery is dirty. Idk what to do.