We study the double charm decays of B-c meson, by employing the perturbative QCD approach based on k(T) factorization. In this approach, we include the nonfactorizable emission diagrams and W annihilation diagrams, which are neglected in the previous naive factorization approach. The former are important in the color-suppressed modes, while the latter are important in most B-c decay channels owing to the large Cabibbo-Kobayashi-Maskawa matrix elements. We make a comparison with those previous naive factorization results for the branching ratios and also give out the theoretical errors that were previously missed. We predict the transverse polarization fractions of B-c --> D-(s)*(+)(D) over bar*(0), D-(s)*D+*(0) decays for the first time. A large transverse polarization contribution that can reach 50%-60% is predicted in some of the B-c meson decays.