An extended variational method for describing the dynamics of a Bose-Einstein condensate （BEC） chirped soliton in the presence of periodic and harmonic potentials is developed. It is shown that the BEC chirped soliton dynamics can be deduced via the extended variational method to a set of four coupled nonlinear differential equations. This deduced set of equations agrees remarkably well with full numerical simulations and highlights the dominant physical interactions in the system, namely amplitude, width, chirp, center-position, and center-frequency dynamics. The extended analytic theory provides a useful, accurate, and greatly simplified description of the governing BEC chirped soliton dynamics. It further gives the critical strength ratio of periodic to harmonic potential necessary to support multiple stable lattice sites for the BEC chirped soliton and demonstrates that the BEC chirped soliton can move selectively from one lattice site to another by simply manipulating the potentials. In addition, some interesting results for the experiments and applications of the BEC are also obtained.