I had read reports that some people lost what they had spent hours typing in, and some had not, when unplugging the unit. I was one who lost everything...probably 10 hours of work. I contacted Sony and you can see their response below. Be careful
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The Sony CDP-CX400 CD changer has an internal rechargeable power supply which powers the memory that holds the user entered data or custom file names. If the unit is left unpowered for over a month, the internal power supply runs down resetting the memory. We suggest that you keep the unit powered all the time to preserve manually entered data.