In the context of a battery holding electrons which carry energy, which we use, what would be the maximum amount of energy that an electron can hold? On what parameters is the energy carried by an electron dependent?

 

Is an electron relating to an atom of one element different from an electron belonging to the atom of another element? Is the capability to hold energy in anyway depend on the atom to which the electron belongs

^{http://en.wikipedia.org/wiki/Electron_rest_mass}

The electron rest mass (symbol: m_e) is the mass of a stationary electron. It is one of the fundamental constants of physics, and is also very important in chemistry because of its relation to the Avogadro constant. It has a value of about 9.11×10⁻³¹kilograms or about 5.486×10⁻⁴atomic mass units, equivalent to an energy of about 8.19×10⁻¹⁴joules or about 0.511 megaelectronvolts.^[1]