Look at the notepad underneath the circles on the wall.
Figure out what number each colored X equals using the number you found earlier.
Green X = 5
Red X = 5
Blue X = 9
White X = 3
Open the cabinet with the White, Blue, Green and Red stripes with the 1's.
White = 3, Blue = 9, Green = 5, Red = 5
Look inside and take the battery.