Jon and Katie King were hesitant about adding batteries to complement solar panels on their Randwick home in Sydney's east but, one month after their purchase, they're already considering buying more.

Lithium-ion battery costs have plunged about a fifth in the past year alone and power prices from the grid are soaring, a combination that is rapidly improving the appeal of energy storage for homes and businesses alike.

Katie King at home with her family's new battery system. Credit:Kate Geraghty

"I'm an advocate in a big way," Mr King, an architect, said. "It's just added another layer of control ... and it's only going to get better."

The Kings' solar panels are slightly under five kilowatts in capacity, supplying about 12-13 kW-hours of electricity a day.