French energy giant Engie has bought an 80% stake in Green Charge Networks, a California-based startup that sells battery systems and software that help building owners store and manage energy.

Engie and Green Charge Networks did not disclose the value the deal or its terms.

The purchase gives Engie, formerly GDF Suez, an immediate position in the battery storage market, while Green Charge Networks gets the money and resources it needs to expand, possibly internationally.

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Green Charge’s standalone battery and solar and battery solutions complements Engie existing business, Frank Demaille, president and CEO of the North American business unit of ENGIE, said in a statement. Green Charge Networks has 48 megawatt hours of battery storage projects either deployed or under construction across more than 150 sites, including commercial properties, schools, and universities.

It also strengthens the company’s other services such as providing power to buildings not connected to the power grid, which is an area of growth for the Engie, Demaille said. Engie has invested in other related companies such as Colorado-based Tendril, a startup that has developed an open, cloud-based platform for managing energy. Earlier this year, it also acquired OpTerra Energy Services, helps companies finds ways to use less energy.

Green Charge Networks is among a growing group of companies that have combined software and low-cost lithium-ion batteries into energy storage systems aimed at helping commercial and industrial building owners lower their electricity bills. The systems are designed to tap into energy stored in the batteries when electricity rates are high during peak hours or on a hot summer day when there’s a lot of demand for power. The battery storage systems have become more important as solar and wind power capacity has increased. For example, when the sun sets, the systems switches from the traditional power grid to the solar power stored in the batteries.

Green Charge is even experimenting with a new business that reuses batteries from Nissan’s LEAF electric car to store energy for commercial and industrial buildings.

AES Energy Storage, Advanced Microgrid Solutions, Greensmith, Stem, and Tesla Energy all sell these battery storage systems.

Energy storage, a seemingly niche business, has attracted increasing attention--particularly after entry automaker Tesla entered into the market--and investment from large multinational power companies like Engie. For instance, battery startup Stem raised $45 million from investors last year, including from the energy trading arm of big German power company RWE Group.