Abstract: This invention uses low levels of light energy as found within dwellings, or other enclosed but lit spaces, to power a device such as a smoke alarm in place of conventional replaceable batteries. Light incident upon a solar cell array (2) attached to a smoke alarm or other battery powered device is collected and converted to a voltage which is multiplied by the action of one or more DC-DC converter circuits (3, 4 and/or 5) to give rise to a resulting output voltage (6). This voltage is applied via resistor (7) and series device (8) to a rechargeable cell or cells (10) and is limited to a maximum voltage by zener diode (9). If desired, a DC-DC converter can be added at the output of the cell (10) in addition to or in place of the DC-DC converter connected to the solar cell. The converter or converters, the regulating circuits and the cell (10) are all housed in a container which is the same size and shape as a conventional dry cell.