Casio DT-900 Operation Manual page 19

3
Remove the old lithium backup battery from
the backup battery compartment with a
ballpoint pen or other fine-tipped object as
shown in the figure on the right. Wipe the new
lithium battery with a dry cloth and then insert
it into the backup battery compartment with
the plus (+) side facing up.
4
Close the cover and tighten the screws.
E-21