John,
I remember reading about back-up batteries on certain keyboards. It was written in the manual in the section that explained how long the was retained in each section of the keyboard. Some for 80 minutes some for a week.

If there is a back-up battery in the Kn6000 the manual would say so – if not I would presume that there is no battery.
It is important to know if the data is lost if the keyboard is switched back on immediately. Also to know what else he is losing when he turns the keyboard on. Is it only Custom Memory, if it is Custom Memory?

On all my Technics I saved every user area the keyboard had.
Current Panel – Panel Memory – Composer – Sound Memory – MSP
Custom rythms – and Midi data.
Before I started playing I would load Current Panel – Panel Memory – Composer – Sound Memory. Custom Rhythms, sequencer and Midi Data only if necessary. I was never concerned about losing the user areas. You can even lose these user areas by loading another party’s Sequence/Data.
Another question: If he is losing the info in a user area what has replaced the lost information?

John C.