Batteries may rewire world's power grids, spell trouble for utility firms

Battery storage technology is nearing a tipping point like the one that accompanied the 'massive' adoption of solar power some years ago, say experts

It's just a marketing gimmick. But it casts a spell.

A pale orange-and-gold sunset bathes the macadamia plantations and avocado orchards that sweep down to Australia's Byron Bay. The coming dusk is a cue for two sleek Tesla battery packs in the garage at Amileka, a secluded holiday villa nearby. They stir silently into action—powering the appliances in the five-bedroom home's twin kitchens, recharging a $100,000-plus Model X SUV, driving a filter pump for an 18-meter swimming pool sparkling in the shade of a century-old native black bean tree.

From first light on this Southern Hemisphere autumn day, a bank of 33