No, the expression you mentioned is not the total energy of an object. The total energy of an object is given by Einstein's famous equation:
E = mc^2,
where E is the total energy of the object, m is its rest mass, and c is the speed of light in vacuum.
In this equation, the rest mass (m) refers to the mass of an object when it is at rest, and c is the constant speed of light in a vacuum. The equation implies that mass and energy are interchangeable and are related by a factor of the speed of light squared.
The expression you mentioned, "half of its rest mass times c squared," is related to the relativistic kinetic energy of an object, not its total energy. The relativistic kinetic energy (K) of an object moving at relativistic speeds can be calculated using the equation:
K = (γ - 1)mc^2,
where γ (gamma) is the Lorentz factor given by γ = 1/√(1 - v^2/c^2), v is the velocity of the object, m is its rest mass, and c is the speed of light in vacuum.
It's important to note that the total energy of an object includes both its rest energy (E = mc^2) and its kinetic energy (K = (γ - 1)mc^2) if it is in motion.