I was wanting to put a battery powered fan on my "little buddy" portable heater, because most of the heat goes up instead toward the area I needed heat, nobody, that I could find, made such a fan. I found a fan that I could make work, but I needed to mount battery(s) to run the fan. the "D" cell battery holder worked perfectly. In my opinion the "little buddy" heater is good, but by the addition of a fan, now it is great.