By land, by sea, and by air, battery power is expanding to drive all kinds of transportation.

The most challenging of these modes may be air travel. It's harder to loft several thousand pounds of batteries into the air, to make them last potentially an hour or more. And if they run out of juice, pilots can't just pull over and call for a tow.

Still, that's what Harbour Air founder and CEO Greg McDougall plans for his fleet of 42 sea planes operating in Vancouver, British Columbia and Seattle.

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The airline made the announcement in March that it plans to convert its whole fleet to electric power using technology from Redmond, Washington-based MagniX, which builds its own dedicated aircraft-quality electric motors. 

MagniX will remove the gas engine from one of Harbour Air's De Havilland DHC-2 Beavers—some of which are more than 50 years old—and replace it with its own 750 horsepower mangni500 motor, rated at 2,075 pound-feet of torque to begin testing this summer, with the aim of converting the rest of Harbour Air's fleet to electric power for commercial runs.

The companies did not specify battery size, but MagniX says it uses state of the art batteries that have 200 watt-hours per kilogram (91 watt-hours per pound.) The batteries will deliver 30 minutes of flight time and 30 minutes of reserve power. That means the first converted sea planes will likely operate on Harbour Air's short hops from Vancouver to some outer islands in British Columbia, which Harbour Air says constitute about 70 percent of its 30,000 flights per year.

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The companies hope to increase that performance to 45 minutes of flight time for a loaded airplane—even eventually one of Harbour Air's larger 18-passenger De Havilland DHC-6-200 Twin Otters—fully loaded for its longest Vancouver-to-Seattle runs.

"We are once again pushing the boundaries of aviation by becoming the first aircraft to be powered by electric propulsion,” McDougall said in a news release. “We are excited to bring commercial electric aviation to the Pacific Northwest, turning our seaplanes into ePlanes.”

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With a focus on its Pacific Northwest audience, Harbour Air bills itself as the first airline to go carbon-neutral in 2007, buying carbon offsets for its operations.

So far, efforts at electric flight have mostly been one-offs, aimed at record attempts or aircraft aimed at a single purpose, such as a helicopter designed to deliver blood in Los Angeles, or package-delivery drones.

Harbour Air is not alone in attempting to electrify. An Israeli startup called Eviation is reportedly working on its first all-electric prototype in France. Harbour Air's effort, however, is the first to use such classic sea planes.