Two examples of the kind of fuel cells that may soon power mainstream laptops were shown at Cebit last month. Both were too bulky to fit inside a notebook case and were rather heavy for the power they delivered.
    But Peter Rabenseifner, head of development at the German firm Smart Fuel Cell, told me: 'We have been reducing the size of our products by 20 per cent a year and we expect this to continue.'

SFC's C25 cell looks about the size of a couple of fat paperbacks stacked together, and weighs 1.1kg. It takes 125ml cartridges of methanol delivering 120 watt-hours of energy and weighing 120g - enough to drive a laptop for a claimed seven hours. But then you can simply swap in another cartridge, making you independent of a mains supply.
    But why not simply have refillable cartridges? Rabenseifner pointed out that methanol is volatile: 'We can't have a risk of fire.' That raises the question of whether these things will be allowed on aircraft.
    Currently CFC's products are available only as auxiliary batteries and were shown at Cebit packed into a pocket in a specially designed laptop case from Consel.
    Toshiba showed a prototype of a similar methanol-driven cell, attached to the back of a Libretto notebook. It was also too bulky (275 x 75 x 40mm) to be anything but an auxiliary battery.
    No total energy figures were given, but it was said to deliver an average 12w (at 11v, 20w peak) and to drive a laptop for 10 hours on 100ml of fuel. But without more detailed figures it was impossible to say whether this meant the Toshiba cell was more efficient.