Radio not working except when car is off

A friend recently acquired a 2013 Prius Plug in. He tells me that he can’t get the radio to work at all when driving, including no Bluetooth. He recently replaced the 12v battery. He did not test radio before replacing battery. Odd thing is that if he parks the vehicle and shuts it down, the radio “usually” works fine.
I have not examined it as he is currently far away from me.
Any ideas what to look at?
Is there something that needs to be reset after battery replacement?

 

I agree that long distance diagnostics are not easy, but all I can do at this point until I see car in person in a few weeks.
Further information I received yesterday. Maybe this will spark some ideas.
If the car is in Ready mode, radio does not power on.
If switched to accessory mode, the radio works fine at least until end of travel. Unknown if Bluetooth works at this point.
But if the car sits for some unspecified time in off mode, the car reverts to non functional radio, unless and utilizes the accessory mode trick is tried.
Sounds to me like the radio is entering a sleep mode or something.