  The two-dimensional organic superconductor $\lambda$-(BETS)$_2$GaCl$_4$
exhibits pronounced charge fluctuations below $T \approx 150$~K, in contrast to
the sibling compound $\kappa$-(BETS)$_2$GaCl$_4$ that remains metallic down to
milli-Kelvin. Infrared spectroscopy reveals only minor splitting in the
vibrational features of the latter compound, common to other strongly dimerized
$\kappa$-salts. When the organic molecules are arranged in the
$\lambda$-pattern, however, a strong vibrational $\nu_{27}(b_{1u})$ mode is
present, that forms a narrow doublet. %indicating static charge imbalance of
about 2\%. Most important, when cooling $\lambda$-(BETS)$_2$GaCl$_4$ below
150~K, two weak side modes appear due to charge disproportionation that amounts
to $2\delta=0.14e$. In analogy to the $\beta^{\prime\prime}$-type organic
conductors, we propose that charge fluctuations play an important role in
emerging of unconventional superconductivity in \l\ at $T_c=4.7$~K. We discuss
the possibility of a charge-density-wave that coexists with the proposed
spin-density-wave state.
