Quarterly Operational Update

Quarterly Operational Update for the three months ended 31 December 2025. QUARTERLY HIGHLIGHTS - HIGH NATIONAL HYDRO INFLOWS – resulted in low wholesale electricity spot prices. - TAUPO STORAGE REMAINS ELEVATED – providing a strong Q3 portfolio position. - NEW OEC5 GEOTHERMAL GENERATION – commissioning started as planned with potential generation upside relative to guidance. COMMENTARY MARKET SUMMARY High national hydrological inflows of 98th percentile was reflected in lower wholesale spot electricity prices averaging $40/MWh in Auckland for the quarter. Forward prices in Auckland for FY26 have eased considerably to $135/MWh due to high inflows and above average hydro storage levels. National demand was up 3.1% for the quarter relative to PCP, primarily due to New Zealand Aluminium Smelter resuming normal operations after a period of demand response curtailments. PORTFOLIO MANAGEMENT HAS PROVIDED A STRONG Q3 STORED HYDRO STARTING POSITION Waikato catchment hydrological inflows were 88th percentile for the quarter, and this resulted in higher hydro generation of 1,072 GWh, up 200 GWh (23%) relative to PCP. Hydro spill was significant at ~345 GWh for the quarter, to maintain lakes within high operating levels. Taupō hydro storage ended the quarter with an above average lake level. Wind generation was 32 GWh (6%) higher for the quarter relative to PCP. Geothermal generation was 50 GWh (9%) lower than PCP (539 GWh compared to 589 GWh) primarily driven by planned maintenance outage at Ngā Awa Pūrua which coincided with low spot prices and was delivered on budget and on time. Commercial & Industrial yield (physical & end-user CfDs) was lower by $3.2/MWh for the quarter relative to PCP. Physical C&I yields were lower as some contracts repriced to a lower 2026 electricity forward curve, while End-User CfDs were lower due to new long-term agreements. Our differentiated bundling and value-creation strategy lifted the share of customers with two or more products by 10% to 223k connections with telco and mobile connections increasing by 30k relative to PCP. WE WILL DELIVER MORE RELIABLE AND RENEWABLE ENERGY WITH NGĀ TAMARIKI OEC5 CLOSE TO COMPLETION Ngā Tamariki OEC5 geothermal expansion is close to completion. Commissioning of the new OEC5 unit started in January and once completed, it will increase site generation by 390 GWh per annum and net output by 46 MW. Full commissioning is expected by the end of Q3. [For Operational Statistics and Charts, please refer to the attached] ENDS Howard Thomas General Counsel and Company Secretary Mercury NZ Limited For investor relations queries, please contact: Paul Ruediger Head of Business Performance & Investor Relations 027 517 3470 investor@mercury.co.nz For media inquiries, please contact: Catherine Morab Reputation and Social Impact Lead 09 282 1158 mercurycommunications@mercury.co.nz