Remove the battery hatch cover to access the battery / ies inside. After that replace the old drained battery / ies from inside with the proper replacement / s.

If your calculator doesn’t have a battery hatch remove the back cover. After removing the back cover, you should instantly see the battery or battery compartment, then replace the old drained battery / ies from inside with the proper replacement / s.

Check out step 3 ( optional ) . Lastly, close up your device, and you're ready to go!