Lithium-ion polymer batteries were investigated. These batteries used microporous PVdF filled by the liquid electrolyte as polymer electrolyte. It has been shown that the conductivity only depends on PVdF porosity, as the contribution of the swollen PVdF structure may be neglected. The loss in conductivity induced by the microporous PVdF is limited while the tortuosity is equal to 1. A shut down effect was demonstrated. Thin and flexible batteries based on this polymer electrolyte meet the specifications of GSM application. (C) 2003 Published by Elsevier Science B.V.