  We present a model-independent global analysis of hadronic form factors for
the semileptonic decays $b\rightarrow c\ell\nu$ that exploits lattice-QCD data,
dispersion relations, and heavy-quark symmetries. The analysis yields
predictions for the relevant form factors, within quantifiable bounds. These
form factors are used to compute the semileptonic ratios $R(H_c)$ and various
decay-product polarizations. In particular, we find $R(D_s^*)=0.20(3)$ and
$R(J/\psi)=0.25(3)$, predictions that can be compared to results of upcoming
LHCb measurements. In developing this treatment, we obtain leading-order NRQCD
results for the nonzero-recoil relations between the $B_c^+ \rightarrow
\{J/\psi , \eta_c \}$ form factors.
