Radio/tape Cd Player problems of the 2015 Subaru Crosstrek

I was driving my 2015 Subaru Crosstrek. I had been on the highway for an hour. I was going about 78mph. The car suddenly started getting loud and the tachometer was revving down. It went quickly from 3 to 0 and immediately shut down. When I realized it was revving down and getting louder I began to shift towards the lanes on the right to the break down lane. My car didn't make it. It was about 3 min from when I realized something was wrong. I got stuck in the lane right next to the passing lane with 2 other lanes on the right of me to get to the breakdown lane. My car had power, my hazards were on, my radio was on, my windows opened and the car wouldn't turn on. I got my car towed to my moms and it turned on at arrival about 14 min after it shut down on me. I was able to drive it home 14 min away and then drive it 35 min to a Subaru dealer. The dealer says its the battery but it doesnt make sense to me if the car ignition wouldn't go on but lights radio and windows worked and 15 min later the car turned on and drove like nothing happened.