A versatile fuel cartridge for storing methanol and water, methanol/water mixture or methanol/water mixtures of varying concentrations is disclosed. The present invention utilizes a filler insert preferably occupying a small portion of the volume of the fuel cartridge, so that the fuel cartridge may hold more fuel to ensure a longer life. The filler insert is capable of wicking and transporting the fuel to the MEA. Additionally, the filler insert remains in physical contact with the fuel in any orientation of the fuel cartridge and at any fuel level in the fuel cartridge. The fuel cartridge may have more than one chamber, and preferably each chamber contains a different concentration of fuel. Optionally, the fuel cartridge may include a pump to initiate fuel flow from the fuel reservoir. The pump may regulate the flow of fuel and importantly to shut off the flow of fuel, when necessary.