There are 3 screws that have to be loosened.
Remove the cover and set it off to the side.
The shiny round disc in the black holder is the battery.
Push the release tab (at the point of the screwdriver) all the way and the battery will pop up.
You have to push flat on the top edge of the tab.
Don't push down, push horizontally.
If you push too low the screwdriver will
prevent the battery from popping up.
You can use your finger nail if you do it right.
The battery's edge will jump up visibly when the catch is released.
Lift the battery out.
This "re-boots" the computer chip and corrects a blank display or other ptoblems.