Help: power black out on Volvo C70 2005

Hello, The symptom on its own is a bit mysterious and could be caused by multiple things. However, the clue I find most helpful is the radio memory concern. If you have a vehicle electrical or charging system issue, you could have this "black out" as you describe, and the "memory" could be lost in the radio as well potentially. Have your battery, charging system, cabling and related components checked for possible issues. However, as you may be aware, if the problem is not occurring, then testing for failure may be impossible.