Toshiba has developed a prototype direct methanol fuel cell, or DMFC, that it says will end the need for rechargeable batteries on portable PCs.The new fuel cell has an average output of 12 watts and a maximum output of 20 watts, and gives about 5 hours of operation with 50 milliliters of fuel, Toshiba said in a statement Wednesday. It runs on replaceable methanol cartridges, Toshiba said.Methanol in a fuel cell delivers power most efficiently when it is mixed with water in a 3% to 6% concentration. To date, this has made the fuel tank too large for portable equipment, Toshiba said. However, the new cell includes a system whereby the methanol is diluted by water produced in the power generation process. This process allows the methanol be stored at a higher concentration, allowing the fuel tank to shrink to a tenth of the size previously needed, the company said.The PC communicates with the fuel cell, giving information on its operating status, so that the fuel cell can balance power demand and supply. Sensors in the cell monitor methanol concentration and tell users when to change the cartridge, Toshiba said.The fuel cell can be directly connected to a PC or other portable device in place of a lithium-ion battery, Toshiba said.Two cartridge sizes have been developed: a 120 gram, 100 milliliter cartridge offering 10 hours of operating time, and a 72 gram, 50 milliliter version giving 5 hours of operation. The fuel cell itself weighs 900 grams, Toshiba said.The DMFCs are expected to be available for sale in 2004, the statement said.