  Lithium ion batteries are attracting significant and growing interest,
because their high energy and high power density render them an excellent
option for energy storage, particularly in hybrid and electric vehicles. In
this brief, a data-driven polynomial nonlinear state-space model is proposed
for the operating points at the cusp of linear and nonlinear regimes of the
battery's electrical operation, based on the thorough nonparametric frequency
domain characterization and quantification of the battery's behavior in terms
of its linear and nonlinear behavior at different levels of the state of
charge.
