  We study the Cauchy horizon (CH) singularity of a spherical charged black
hole perturbed nonlinearly by a self-gravitating massless scalar field. We show
numerically that the singularity is weak both at the early and at the late
sections of the CH, where the focusing of the area coordinate $r$ is strong. In
the early section the metric perturbations vanish, and the fields behave
according to perturbation analysis. We find exact analytical expressions for
the gradients of $r$ and of the scalar field, which are valid at both sections.
We then verify these analytical results numerically.
