The prospect of small fuel cells replacing batteries in portable equipment is considered in terms of their prospective energy density, technological feasibility, safety and cost. Fuel cells seem to be best suited to applications where significantly more energy storage is required than at present in portable devices (>20 Wh). Energy requirements (Wh) are likely to increase with the introduction of broadband mobile computing, and fuel cells with lightweight fuel supplies could dramatically increase the amount of energy available in the same volume. However, in contrast to batteries, since the energy source and the energy converter are separated, a fuel cell system adds complexity and associated safety and reliability issues will need to be carefully assessed for portable applications. However, the prospective commercial market for high energy density power sources is attractive enough to support significant development and accelerate the introduction of small fuel cells since battery technology is unlikely to be able to meet the growing energy demands of a mobile workforce.