Generators have stayed the same since their first use on MMVs. They supply additional power that allows MMVs and MAVs to operate parts with a high energy requirement. They come in three categories based on energy production. A MAV can equip multiple generators without any diminishing returns to fit their energy requirements. A single heavy generator could be replaced by two medium generators depending on the requirements of the operator.
Physically the smallest and worst power to weight ratio generators in the game. They are great for when you just need a few hundred units of energy. You'll notice them on a lot of light builds like those using Wheeled or Hover chassis.
Stepping it up these are generally the most versatile generators with their relatively small profiles and their variety of shapes and connection points.
The best energy to weight ratio generators, these are usually reserved for heavy energy requirement builds due to their weight.