You might have a faulty battery which would need to be replaced (these are soldered in and need to be replaced by an authorized service center I believe) I had several bad batteries a few years ago on many WK6 and WK2 keyboards which needed to be replaced.
George Kaye
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George Kaye
Kaye's Music Scene (Closed after 51 years)
West Hills, California
(Retired 2021)