This can only be the case if  Specializing to the case that formula_24 is a fixed reference temperature: the temperature of the triple point of water. Then for any "T"2 and "T"3,  Therefore, if thermodynamic temperature is defined by  then the function viewed as a function of thermodynamic temperature, is and the reference temperature "T"1 has the value 273.16. (Of course any reference temperature and any positive numerical value could be used—the choice here corresponds to the Kelvin scale.) It follows immediately that Substituting Equation back into Equation gives a relationship for the efficiency in terms of temperature:  Since fuel cells and batteries can generate useful power when all components of the system are at the same temperature (formula_34), they are clearly not limited by Carnot's theorem, which states that no power can be generated when formula_35. This is because Carnot's theorem applies to engines converting thermal energy to work, whereas fuel cells and batteries instead convert chemical energy to work. Nevertheless, the second law of thermodynamics still provides restrictions on fuel cell and battery energy conversion.