Hi Jean,

I don't think that the 6000/6500 uses a Lithium battery, but probably a memory backup capacitor that will run down over the course of a few weeks if the keyboard is not powered. I seem to remember the manual stating that settings such as panel memories will be remembered for about a week, but I have left my machine off for over a month at a time and all has been intact when it was repowered. I did once have a KN5000 lose some settings though. As you say, lithium batteries are good for several years, so there is no reason why the manual would state typical retention times for certain settings if such a battery was used.
Some settings such as the Custom Styles and Midi setups are stored in non-volatile flash memory which lasts forever (or at least until you overwrite it with something else!)

Regards,

Richard.