**5.1 Experimental analysis**

Identification of a linear model may be delicate, but there are a lot of classical well trained methods for this.

For a non linear system, it is difficult to find a general approach.

For most cases, it is possible to separate steady state non linear set point positioning, then local small signal linear investigation.

For battery, the set point should be defined by the state of charge and the operating current. But the fact that when you apply a non zero operating current, the state of charge is no longer fixed. This is an important practical problem, all the more critical as there is a the strong dependence of the activation impedance with respect to the current. The experimental methodology presented is centered on this non linearity topic.
