18650 can explode in rare situations and it happend to many of us. There is a tread just about that. Something like that happend to one German cyclist. Because of the pressure of escaping gas from faulty? Overcharged? 18650 batteries , closed tube of little torch light exploded with a lot of damage to this guys kitchen and his both hands and arms. His skin was cut to his bones. There is a lot of pictured showing the damage.

My 3 AAA batteries are 1.5 v each , and this torch shines at full power for good couple hours, and after that for another 2-3 hours of good light safe enough for 15 mph ride. Still, I change batteries every 10 hours or so. When its cold, they don't last that long.

My magicshine battery pack is 2x 18650, but its in open design case, so if it blow for any reason ( moisture for example ) gas will easily escape without throwing pieces in my face or hands.
I would recommend buying 18650 from big, well known companies like Panasonic or Samsung, and only protected ones.