Battery drain is almost nothing. The game doesn’t need to be opened when you walk, and you can kill it entirely. The pedometer is anyways running on most phones regardless if you have WalkScape installed or not, so this doesn’t add battery consumption in that sense either.
For me when I just checked, it’s used less than 0.3% today which is less than most other apps I have installed. I’ve tried my best to keep this as low as possible, and we’ll probably be optimizing this even further in the future if necessary.