Loading the file from disk introduces a slight dependency on the working
directory for the simulator. Prevent that by loading the bmp from
memory.
Use a python script to convert the backround bmp image to a C header
file. Include this header in `main.cpp` and load the bmp from memory.
Instead of drawing just circles use a background image to show status
symbols what the respective status means (not just the color of the
dots).
Furthermore draw a rectangle for the battery status instead of bubbles.