Brazil is going through a decisive moment in the regulation of Energy Storage Systems (SAE). The National Electric Energy Agency (ANEEL), through Public Consultation 39/2023 and the subsequent Joint Technical Note 13/2025, has been building the normative bases to integrate batteries, reversible plants and other storage systems into the National Interconnected System (SIN). The central point of the debate is the definition of how these enterprises should contract and remunerate the use of the electricity grid, a point that involves pricing, concessions, sectoral charges and regulatory equality. The approval of Law 15,269/2025 formalized the legal framework, but infralegal regulation still depends on ANEEL decisions that test the consistency of the Brazilian regulatory model in the face of technological innovation.