NOVELTY - A liquid-activated battery (110) comprises greater than or equal to 1 hydrogel (115) which consists of greater than or equal to 1 hydrophilic polymer and greater than or equal to 1 electrolyte (120) and is configured to recurrently alternate between hydrated state responsive to contact with liquid and dehydrated state responsive to effective absence of liquid and greater than or equal to 1 anode (130) and greater than or equal to 1 cathode (125) which are in contact with greater than or equal to 1 hydrogel. The ionic communication between anode and cathode via greater than or equal to 1 electrolyte is supported by the hydrogel in hydrated state and is not supported by the hydrogel in dehydrated state and generates an electric current for the battery.    USE - A liquid-activated battery for electronic device, such as sensor, actuator, processor, switch, light source, alarm, receiver, transceiver, transponder, and/or radio-frequency identification device which are configured to operate in underwater environment and embedded in a wetsuit (all claimed).    ADVANTAGE - Hydrogel is dehydrated such that ionic communication does not occur between anode and cathode. The liquid-activated battery may continuously alternate between active state and dormant state by exposing the battery to liquid and allowing the battery to dry.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) electronic device (105) comprising power supply which contains liquid-activated battery (110);    (2) preparation of liquid-activated battery which involves providing greater than or equal to 1 hydrogel (115) and arranging greater than or equal to 1 anode (130) and greater than or equal to 1 cathode (125) to be in contact with the greater than or equal to 1 hydrogel; and    (3) providing battery power to electronic device using liquid-activated battery which involves connecting the battery as power source to the electronic device and exposing the battery to liquid such that the liquid contacts the hydrogel which enters the hydrated state for the battery to generate a voltage operative to power the electronic device.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a liquid-activated battery.    Electronic device (105)    Liquid-activated battery (110)    Hydrogel (115)    Electrolyte (120)    Cathode (125)    Anode (130)