  We study analytically the Cauchy horizon singularity inside
spherically-symmetric charged black holes, coupled to a spherical
self-gravitating, minimally-coupled, massless scalar field. We show that all
causal geodesics terminate at the Cauchy horizon at a null singularity, which
is weak according to the Tipler classification. The singularity is also
deformationally-weak in the sense of Ori. Our results are valid at arbitrary
points along the null singularity, in particular at late retarded times, when
non-linear effects are crucial.
