The PSR-540 Owner's Manual has the following para on page 2.

"Battery Notice:
This product MAY contain a small non-rechargeable battery
which (if applicable) is soldered in place. The average life
span of this type of battery is approximately five years.
When replacement becomes necessary, contact a qualified
service representative to perform the replacement."

I have no info on the KN650 but the KN6000 and KN7000 both appear to use capacitors which are soldered.

Len