  Fluid flows in liquid metal batteries can be generated by a number of
effects. We start with a short overview of different driving mechanisms and
then address questions specific to the metal pad role instabilities in
three-layer systems. We focus on the role of the conductivity distribution in
the cell, noting at the same time that interfacial tension should be considered
as well for smaller cells. Following this discussion, numerical results on the
excitation of interfacial waves in two-layer liquid metal systems with
miscibility gaps bearing an interface normal electric current are presented.
Confirming recent results from the literature, we find that magnetic damping
plays a decisive role for strong vertical magnetic fields. In addition,
boundary conditions for the electric field strongly influence critical currents
and growth rates.
