If I recall correctly, this model has a small, storage battery that is mounted upon the mother board, which is not easy to get to. Pretty typical of keyboards of that era. If the battery dies, so does the internal memory storage, which limits the usage of the keyboard to floppy storage only, but even this may not be functional without the battery working.
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.)