Should I include research stays in my CV?
Yes, listing them would add some more value to the CV.

This is how I would list it in my CV under a section called Research Visits.

Research Visits


Visiting researcher, ABC Laboratory, University of Alphabets (Duration: January 01 -- January 09, 2018; Supervisor/Collaborator: Professor A. BCDEG)
Visiting researcher, ABC Laboratory, University of Alphabets (Duration: January 23 -- January 30, 2018; Supervisor/Collaborator: Professor A. BCDEG)