  We study the mathematical properties of a general model of cell division
structured with several internal variables. We begin with a simpler and
specific model with two variables, we solve the eigenvalue problem with strong
or weak assumptions, and deduce from it the long-time convergence. The main
difficulty comes from natural degeneracy of birth terms that we overcome with a
regularization technique. We then extend the results to the case with several
parameters and recall the link between this simplified model and the one
presented in \cite{CBBP1}; an application to the non-linear problem is also
given, leading to robust subpolynomial growth of the total population.
