def METHOD_NAME(self, variables):
    param = self.param
    c_e = variables["Electrolyte concentration [mol.m-3]"]
    c_e_conc = variables["Electrolyte concentration concatenation [mol.m-3]"]
    T = variables["Cell temperature [K]"]
    tor = variables["Electrolyte transport efficiency"]
    i_boundary_cc = variables["Current collector current density [A.m-2]"]
    def flux_bc(side):
        # returns the flux at a separator/electrode interface
        # assuming v_box = 0 for now
        return (
            pybamm.boundary_value(
                -(1 - param.t_plus(c_e, T)) / (tor * param.D_e(c_e, T) * param.F),
                side,
            )
            * i_boundary_cc
        )
    if self.options.whole_cell_domains[0] == "negative electrode":
        # left bc at anode/current collector interface
        lbc = pybamm.Scalar(0)
    elif self.options.whole_cell_domains[0] == "separator":
        # left bc at anode/separator interface
        lbc = flux_bc("left")
    if self.options.whole_cell_domains[-1] == "positive electrode":
        # right bc at cathode/current collector interface
        rbc = pybamm.Scalar(0)
    # elif self.options.whole_cell_domains[-1] == "separator":
    #     # right bc at separator/cathode interface
    #     rbc = flux_bc("right")
    # add boundary conditions to both forms of the concentration
    self.boundary_conditions = {
        c_e: {"left": (lbc, "Neumann"), "right": (rbc, "Neumann")},
        c_e_conc: {"left": (lbc, "Neumann"), "right": (rbc, "Neumann")},
    }