Bmw E90 starting issues

Any insight or thoughts would be appreciated. I have had my 335 sitting in the
garage for about 3 months, just stored for winter and some maintenance. The
car was turned on occasionally to run for a couple of minutes. Recently, I tried
taking the car out to drive and went the gas station, shutting the car off. After
trying to turn the car back on, it would not turn over, ignition was on but no
power. I tried jumping the car, charging the battery but no luck. After a few
hours, the car started up again and I drove it back home. Then after turning it
off again, it would not start. Any ideas or thoughts on what it could be? Battery
is very new.