For me, in normal use, I'm somewhere around a max of 4 18650's; but, the overall bulk and weight of the light matters. My Noctigon M43 with 4 cells is downright tiny compared to many other 4x18650's, and gets a lot of use due to its form factor and size--on my bike handlebar, around the house, in the car. At the other end of the size spectrum, my BLF GT with the short tube also has 4x18650's, and is really just a 4-lb. toy I bring out when I want to giggle at a local lake, car camping, etc. (someone else called it "Hulk's light," which I really like).