NOVELTY - A fuel cell (100) to supplement electrical power in an aircraft, comprises a replaceable fuel cartridge (204); a replaceable by-product cartridge (206); an information output to output information; and a power output to output power to the aircraft. The fuel cell further comprises a main body (202) where the main body may receive at least one of the replaceable fuel cartridge or the replaceable by-product cartridge. The replaceable fuel cartridge comprises a solution containing methanol and/or bacteria.    USE - As a fuel cell to supplement electrical power in an aircraft by outputting power to a line-replaceable unit of the aircraft (claimed); useful to supplement electrical power in variety of applications, such as ground vehicles or any situation in which supplemental power is needed.    ADVANTAGE - The fuel cell supplementing power to an aircraft line-replaceable unit (LRU) can extend the functional duration of the LRU by a significant measure, such as by 6-8 hours. The fuel cell is lightweight relative to an equivalent battery configuration.    DETAILED DESCRIPTION - A fuel cell (100) to supplement electrical power in an aircraft, comprises a replaceable fuel cartridge (204); a replaceable by-product cartridge (206); an information output to output information; and a power output to output power to the aircraft. The fuel cell further comprises a main body (202) where the main body may receive at least one of the replaceable fuel cartridge or the replaceable by-product cartridge. The replaceable fuel cartridge comprises a solution containing methanol and/or bacteria. The replaceable by-product cartridge comprises an absorbent material. The replaceable by-product cartridge comprises a replaceable water cartridge. The information output comprises an information output to output a fuel cell on indicator, a remaining charge measure, and/or a remaining time measure; or an information output to output ARING 429 bus data, Military Standard 1553 bus data, Ethernet bus data, and/or USB bus data. An INDEPENDENT CLAIM is included for supplementing electrical power in an aircraft, involving providing a fuel cell in the aircraft; and supplementing an electrical power system of the aircraft with power generated by the fuel cell by outputting power from the fuel cell to the electrical power system.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a fuel cell.    Fuel cell (100)    Main body (202)    Replaceable fuel cartridge (204)    Replaceable by-product cartridge. (206)