In version 0.0.22 there is the option to use sounds when opening the slide.
This is very poorly implemented and causes the high cpu usage.
I am now testing the next version, which hopefully solves this problem.
Note: it does not matter whether the sounds are turned off, since the
pygame.mixer is still initiated.

The version I am now testing, will unload the mixer if sounds are not enabled, which sound stop the battery drain.

I will make the new version available today so you can test it.

For the impatient: version 0.0.21 should not have this issue.