In the low power range, from a few milliwatts to some hundred watts, fuel cells are potential substitutes for today’s rechargeable batteries. The portable business has been one of the fastest-growing markets over the last decades. Lap-tops, mobile phones, handheld cameras and other small electrical devices are sold in millions each year. 

In addition to dimensional factors like size and weight, properties such as operating, response and start-up time are the most important characteristics relating to portable devices. The integrated power source also has to have a suitably low operating temperature, so the PEMFC and the DMFC are the only two types which are considered. Compared to batteries, the separation of the converter and the fuel tank in fuel cell systems results in more freedom during the design phase. The size of the fuel cell itself determines the maximum power output while the amount of fuel in the tank limits the operating time (or in other words maximum energy). For batteries, both power and energy are closely connected to the geometric design. A lap-top uses a minimum of 20 W and can normally be operated for 2-3 hours, while mobile phones only need 2-5 W and have a standby time of at most 10 days. Fuel cells have a higher theoretical energy density than today's batteries, and in contrast to the relatively long recharging time for batteries, fuel cells are “recharged” by refilling the tank. 

After some time of operation, the capacity of rechargeable batteries decreases due to the many charging cycles. More research has to be done to confirm this, but fuel cells potentially have a much longer lifetime. Due to the separation of the fuel converter and the tank, self-discharging is also not a problem. Both PEMFC and DMFC are considered to be promising for portable applications. Their advantage compared to other fuel cells is the high power output at low operating temperatures. The PEMFC offers the highest power density of the fuel cell stack, but is still limited in respect of storage of hydrogen. Metal hydrides, which are mostly used, suffer from high weight as the content of hydrogen is only some weight-percent. Liquid methanol has a very high energy density and is also easy to store. However, the DMFC has a much lower power density than the PEMFC and usually has to operate with diluted methanol (methanol and water mixture). Due to the liquid fuel, the DMFC system is simpler than the PEMFC. The choice of fuel cell type depends on the application and operating conditions.

The development in the portable business is still growing strongly, and more features are added to the applications all the time. This of course increases the demands on the power source. Forecasts indicate that today's battery technology no longer will be able to keep up with the power requirements. Fuel cells are likely to enter the portable market, but there are still some problems that have to be solved. Most of the early prototypes were PEMFC, which have experienced problems with heat and water management. In the last couple of years, there has been more focus on DMFC. Before any of the fuel cell systems are preferred to batteries, improvements must be made concerning size, water, carbon dioxide (for DMFC) and heat management, operating stability and of course costs. 

Almost all portable electronics companies are involved in fuel cell research and many have presented some results or a complete prototype. In addition, there are several companies and research institutes working on fuel cells in the low power range. There are already many companies that have passed their first announced date for releasing fuel cell product. At the moment, a more realistic forecast is that the first fuel cell powered portable applications will become available in 2004/2005. 

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