  A mechanical analogy is used to analyze the interaction between the magnetic
field, electric current and deformation of interfaces in liquid metal
batteries. It is found that, during charging or discharging, a sufficiently
large battery is prone to instabilities of two types. One is similar to the
metal pad instability known for aluminum reduction cells. Another type is new.
It is related to the destabilizing effect of the Lorentz force formed by the
azimuthal magnetic field induced by the base current and the current
perturbations caused by the local variations of the thickness of the
electrolyte layer.
