Minis from G.I. Joe are mini-Battle Android Troopers. (We can call them mini-BATs to save space, though.)
According to creator Tungsten Monk (via e-mail), the mini-BAT's appearance is based on "the basic Mark 0 version that appeared in the G.I. Joe 'Real American Hero' comic series . . . Basically, they look like standard Cobra blueshirts with added funky full-face helmets and random electronics here and there. (I gave Sargent Commander a coalscuttle helmet because their design varied a lot between appearances, but this pic (on the right) is a good example of the default for the Mark 0.)"
Due to being programmed with the thought processes of comic book/90s cartoon terrorists, mini-BATs can be provoked into aggression by mentioning things like "justice" or "freedom," but will act particularly loyal towards agents who themselves display destructive or villainous tendencies.
Battle Android Troopers are mechanized soldiers created by Cobra to serve as ground troops. They are cheap, mass-producible soldiers that always obey orders and don't retreat. They are also mindless, unable to recognize foe from ally and shooting anything that moves. The exception is Overkill, a BAT with special tactical and analytic programming who serves as the commander of the other BATs.