Ive jumped it twice and let it run for 15-30 minutes after it starts and after l shut it off 20 minutes later it wont start.

you need to do a voltage draw test. something is not turning off. also have your battery tested.

take out the battery and charge it, then you can load test it. clean or replace the cables, it it still wo not hold a charge, it is probably the diodes or rectifiers in the alternator, you can rebuild it or replace it..

one step at a time..