UN GTR No. 25 on In-vehicle Battery Durability for Electrified Heavy Duty Vehicles provides harmonised methods to determine battery durability performance of HD-PEVs and HD-OVC-HEVs of categories M₁-M₃ and N₁-N₃ exceeding 3,855 kg MPLM. The regulation requires manufacturers to install State of Certified Energy (SOCE) monitors throughout vehicle lifetime. In-use verification consists of Part A verification of monitor accuracy through measured UBE testing using Methods 1a, 1b, Method 2 (bidirectional power supply), or an alternative HDV chassis dynamometer method, with statistical pass/fail criteria. Part B verification assesses battery durability against optional Minimum Performance Requirements (MPRs) through remote SOCE data collection from sample vehicles. Part C verification, reserved for future amendment, will address reported virtual distance accuracy for V2X, PTO and non-traction purpose applications. Optional Annex 4 specifies MPRs by vehicle category and mass, ranging from 45-70% SOCE retention across specified timeframes and distances. The GTR entered into force with Phase 1 covering core durability assessment and data collection to support future refinement of MPR thresholds based on in-service field data relating to HDVs, referencing WP.29-170-31 and GRPE/2026/3.