A novel method and system for determining state of charge of a battery is disclosed wherein the direct method and the indirect method are not used at the same time, but alternately as indicated by battery current status. An etching method of the present invention includes bringing the etchant into contact with at least one metal selected from nickel, chromium, nickel-chromium alloys, and palladium. The third capacitor dumps through a silicone controlled rectifier to short the second capacitor to ground, to decrease the level of energy stored by the second capacitor. The invention additionally provides for use of isolated and purified CDPs to induce antibodies and to screen libraries of compounds and use of anti-CDP antibodies in diagnostic assays.