In the past few years, Bill Gates has already invested in three energy storage companies — MIT spinout Metal Battery (renamed Ambri), Berkeley-based LightSail Energy and Bellevue-based TerraPower.

Now, the Microsoft co-founder is putting his money to a fourth. Pennsylvania-based Battery maker Aquion Energy announced a $35 million funding round today that includes Gates as a new investor.

The amount Gates invested was not disclosed. This round was led by Bright Capital, a Moscow-based venture investor, and also included Gentry Venture Partners along with previous investors Kleiner Perkins Caufield & Byers, Foundation Capital and Advanced Technology Ventures.

Aquion was founded in 2008 and develops batteries that use basic, nontoxic materials like saltwater, cotton, dirt and carbon to conduct electricity for stationary applications. The company says that this method is better for the environment, cheaper and more sustainable than acid or alkaline.

Back in 2011, Gates penned a blog post titled: “We Need a Battery Miracle.” Then, speaking at at The Wall Street Journal’s ECO:nomics conference in Santa Barbara, California in early 2012, Gates noted that “cheap energy is like a fantastic vaccine.”

geekwire.com