I'm not sure if it's true, but I was told there was a small, internal battery on the main board that was similar to a cmos batter in a computer and the life expectancy was about 7 to 10 years. If it's similar to my PSR-5700, once it dropped dead, you had about two days to replace it before the storage capacitor lost the information and the keyboard had to be reprogrammed. If I ever have to take one of my 2000s apart, I'll check the board and post the information here.
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)