BattleMechs are armored bipedal, or quadrupedal, military units in service to the various planetary and multi-planetary nations of the Inner Sphere, greater Periphery, Kerensky Clans, various Mercenary or Pirate groups, and the CSN. Original based upon IndustrialMechs developed during the years of the Terran Alliance prior to the discovery of K-F drives, it would take until 2439 and the combined efforts of over twenty of the Terran Hegemony's largest defense contractors to create the first true BattleMech, the Mackie. Since that time, BattleMechs have come to dominate the battlefields of the Inner Sphere, and other regions of the greater Periphery as yet unknown to the Inner Sphere proper. Or at least not any that are publicly acknowledged.
BattleMechs normally weigh in between 20 and 100 metric tons, in 5 metric ton standardized increments for ease of both categorization, and to allow multiple parts sharing between 'Mechs of different types. Virtually all 'Mechs in service have parts commonality between other units of the same mass, such as actuators, myomer bundles, certain internal structure frameworks, etc. All BattleMechs utilizing fusion reactors must have combat rated heat sinks to disperse thermal buildup generated from both weapons fire, myomer friction during movement, and from the reactor itself. Failure to keep a regulated temperature can result in a runaway destabilization of the reactor core's magnetic field resulting in a catastrophic breach of the containment unit. While not generally hazardous in and of itself as the fusion bottle will quickly disperse due to lack of mass, several of the components used in 'Mech construction are highly volatile at extreme temperature ranges normally found in a fusion reactor. When the released plasma touches these components it can result in an explosive event in the sub-kiloton range, near vaporizing the 'Mech itself, along with anything else within several hundred meters. While in the Inner Sphere, Periphery, and Clans, this is generally referred to simply as a 'Core Breach', within the CSN's GDI, it is commonly known as a 'Stackpoling' due to undisclosed reasons.
The generally accepted shorthand name for a BattleMech is 'Mech, with an apostrophe before the word proper. When spelled out completely as BattleMech, the 'M' in mech is to be capitalized. It is not to be spelled as 'Battlemech', however common in media it is for this to be printed in this fashion, it is incorrect.