India’s hidden battery fleet can keep the lights on

One of the crucial factors keeping India’s lights on when the temperature at dusk soars above 40 degrees Celsius (104 Fahrenheit) rarely gets discussed. And yet they’re everywhere in the world’s third-biggest power market.

Inverter batteries — low-voltage lead-acid systems, capable of charging up from a wall socket and powering a few lamps, some fans and perhaps a television for a few hours when the power drops — are a product of decades of unstable grid power. They’re a quiet, clean replacement to the diesel generators that were ubiquitous in earlier decades. Now, more powerful lithium-ion units are promising yet another revolution.