The world is using less oil today to generate electric power than it did in 1973, despite output almost trebling to 17.5 billion watt hours of electricity, from 6.1 billion WH.

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The result is a material that has an energy density of about 0.005 watt-hours per kilogram.

ECONOMIST: Carbon-composite batteries

And by covering the fibres with carbon nanotubes, at least 20 watt-hours per kilogram is expected by the end of next year.

ECONOMIST: Carbon-composite batteries

Not much, admittedly, when compared to the 128 watt-hours per kilogram of a lithium-ion battery, like that found in many electric cars.

ECONOMIST: Carbon-composite batteries

The Turbo battery has 342 Watt-hours of real capacity, meaning that all of this energy can actually be used by the rider instead of some theoretically possible calculated number.

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Virtually nothing at national levels is stored as electrons, not even at your iPad level where watt-hours are stored in batteries in an intermediate form as ionized chemical molecules.

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The two-watt Atom chip inside the Series 5 is rated for about nine hours of battery life, whereas the Core i5-powered Series 7 is expected to last between four and five hours on a charge. (The Series 5 is lighter, too, at 1.65 pounds, compared with 1.89 for the Series 7.) And, being a lower-powered device, the Series 5 has no vents.

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The 48 Watt charger will rapidly bring the battery to full capacity in about 2.5 hours.

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