Safety is the first priority in lithium ion (Li-ion) battery applications. This paper deals with a possibility of the usage numerical simulation methods (by using Finite element/volume method) for application in the advanced sources of electrical energy. These methods are useful in batteries (lithium-ion, lead-acid, etc.), solar panels, fuel cells, etc. It is possible to simulate electro-chemical reactions, current fields, temperature fields, electric potentials, concentrations gradient, electromagnetism, charging and discharging cycle, etc. This paper demonstrates the usage FEM and FVM methods in solution of thermal field of lithium ion battery by discharging. These results can be used in the future as initial conditions for structural analyses, nail test simulation, etc.