I love the backstory for this poor Roomba! XD I felt like I was able to understand the mechanics pretty quickly as well which was great.
One thing I'd suggest is to decrease the amount of area that needs to be move over on the dirty areas for them to become clean. I found myself having to backtrack multiple times, especially on the large areas, which may be more accurate for what a Roomba actually does but it started to feel repetitive after a bit and detracted from the actual puzzle solving which is where this game really shines!
I also think keeping the visual of # of charges is useful information for the player when making decision about what to do next in a level.
I hope you keep working on this! It's a great little puzzle game!