  The $10$ GHz microwave conductivity, $\sigma(T)$ and high field, $222$ GHz
electron spin resonance (HF-ESR) of Li$_4$C$_{60}$ fulleride is measured in a
wide temperature range. We suggest that the majority of ESR active sites and at
least some of the charge carriers for $\sigma(T)$ are electrons bound to a
small concentration of surplus or vacancy ions in the polymer phase. Both
$\sigma(T)$ and the ESR line shape depend on ionic motion. A change of the
activation energy of $\sigma(T)$ at $125$ K coincides with the onset of the
ionic DC conductivity. The ESR line shape is determined mainly by Li ionic
motion within octahedral voids below $150$ K. At higher temperatures,
fluctuations due to ionic diffusion change the environment of defects from
axial to effectively isotropic on the ESR time scale. $\sigma(T)$ data up to
$700$ K through the depolymerization transition confirm that the monomeric
phase of Li$_4$C$_{60}$ is a metal.
