Well 2 x AA fit lengthwise perfectly and would give you about 160 lumens.
Not as bright as other configs...but still quite bright. I generally get over 1 hour of runtime from 2AA's....then a diminishing moon mode
I did some testing on my M30 the other day
2AA(multiple brands of alkaline).....current draw is almost 1A...actually .096-.098a
17500 Li-ion...draws 1.29-1.3A
and just for the hell of it 3AA.....current draw was over 1.4A
and man was it bright.....Kind of a long setup, would require a tube of 5xcr123 length and a small spacer
I think I will get another 1 cell extender and give this setup a blast
could double as a walking cane too