Tesla’s Quiet Moneymaker, Its Battery Business, Suddenly Stalls

The company’s energy storage sales saw rapid growth, until an unexpected slowdown this year.

Tesla Megapack batteries at the Victorian Big Battery site operated by Neoen SAS near Melbourne, Australia.

Photographer: Carla Gottgens/Bloomberg

For years, one aspect of Tesla Inc.’s business has been growing outside the public eye, its revenue soaring even as the company’s electric car sales sputtered and stalled.

Now analysts wonder if Tesla’s quiet moneymaker faces problems of its own.