As scorching weather envelops the Northeast and the Midwest, electric utilities are scrambling to keep the power on while air-conditioners strain utilities’ capacity. By Tuesday afternoon in New York City and Westchester County, for instance, Consolidated Edison had logged nearly 7,700 interruptions since the heat arrived on Sunday, and it had dispatched crews to restore almost all of the power.

Such disruptions have plagued utilities for years: how do they keep extra electricity on hand and ready to go, avoiding the need to cut the voltage in stressed neighborhoods and lowering the risk of blackouts?

Now, several utilities, including Con Edison, National Grid and the large European utilities Enel and GDF SUEZ, have signed up to fine-tune and test what they hope could lead to an answer — a battery half the size of a refrigerator from Eos Energy Storage, the company said Tuesday. If the testing goes well, the batteries hold the promise of providing storage that until now has been unaffordable on a large scale.

“Energy storage is no longer an idea and a theory — it’s actually a practical reality,” said Steve Hellman, Eos’s president. “You’re seeing a lot of commercial activity in the energy storage sector.”