A commercial sheet of paper based on natural cellulose fibers acting as permeable membrane with thin film metal cathode (Cu) and anode (Al) layers in each face was used to produce paper batteries that could be interconnected in series and rechargeable using water as electrolyte. Their electrical characteristics and the set of electrochemical reactions that support the experimental behavior observed are described in this paper. A series of integrated batteries able to supply a voltage of about 3 V and a current ranging from 0.7 mu A to 25 mu A in cells with sizes of 1.2 cm x 3.0 cm for a relative humidity in the range of 50-65% were produced in a single sheet of paper, and successfully applied to control the ON/OFF gate state of paper transistors. (C) 2010 Elsevier Ltd. All rights reserved.