Fuel cell maker ReliOn has scored an additional $6 million in financing from existing investors, money that will be used to expand sales and marketing efforts in the U.S. and overseas. The Spokane company — which has delivered its back-up power systems to more than 1,200 customers worldwide — is led by former Metawave Communications CEO Gary Flood.

“This is an exciting time for ReliOn,” said Flood. “In 2010, we experienced year over year tripling of both sales and gross profit as a percentage of sales. With this funding, we are able to accelerate a number of important programs currently underway which move the company toward our objective of becoming the first profitable fuel cell company.”

Backers of the company include Montlake Capital, Robeco, Oak Investment Partners, Chrysalix Energy Venture Capital LP and others. Formerly known as Avista Labs, ReliOn is a spin-off from Spokane utility Avista. The company is heavily-funded, having previously raised rounds of $20 million and $25 million in the mid-part of the last decade.

The company’s fuel cells are used as back-up power sources for cell towers, aviation systems and other critical infrastructure. ReliOn employs 47 people.

Update: The company says total capital raised since the spin off from Avista in 2003 now stands at $86 million.

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