Brazil’s first large-scale battery energy storage auctions, scheduled for December 2026, are proceeding under a cloud of significant regulatory uncertainty, as the country’s electricity regulator, the National Electric Energy Agency (ANEEL), scrambles to finalize the controversial rules for allocating the costs of the new grid capacity. The core of the problem lies in defining who will bear the financial burden—power generators or a potentially broader base that could eventually include millions of ordinary Brazilian electricity consumers.