According to the Evolv spec sheet, the 250 comes with reverse polarity protection, so those "manual reverse polarity protection" rings are not required.
"If you are manufacturing a device that is designed to be used with three individual replaceable 18650 cells, the DNA250 now offers reverse polarity protection."
from https://downloads.evolvapor.com/dna250.pdf
"If you are manufacturing a device that is designed to be used with three individual replaceable 18650 cells, the DNA250 now offers reverse polarity protection."
from https://downloads.evolvapor.com/dna250.pdf