SMC_F150

I have a 2013 F-150 XL with the Sirius-capable audio system with SYNC. A few weeks ago I started getting Battery Management System (BMS) messages about a low battery, and the audio system eventually shut down. I recharged the battery from 8V to 12V+, and my Ford dealer reset the BMS without charge. The audio system is still shut down. When I try to turn the radio on, the time will blink on, then off and stay off. I have the small display below the dash. All it shows is a small Bluetooth icon when the ignition is on, and the outside temperature. I searched the forum, but could not find this problem. I checked the relevant fuses, and none were blown. Any help appreciated. The Ford dealer can't get to me for a month.