A Core Overload Grenade is a piece of equipment employed by Pilots of the Frontier Militia, as an Anti-Titan weapon. In performing a manoeuvre known as a "Nuke Rodeo", Pilots insert the Grenade into the Titan's Battery slot, overloading the core and causing to explode in a nuclear fireball almost immediately.
The Grenade's visual appearance resembles a regular Battery, but coloured red as opposed to the standard green. It is possible this is an ad-hoc modification to regular batteries created by Militia technicians.