T he 240v dc system is a critical component in providing backup power to the gas turbine 4.1 unit at the muara tawar pltgu, especially during emergency conditions (blackouts). the battery in this system functions as a temporary power source before the emergency diesel generator (edg) is activated. this study aims to evaluate the battery capacity against the load on the 240v dc system and to analyze battery performance under both normal and emergency conditions. the methods used include load calculations based on actual operational data and battery capacity analysis using the ieee 485-2020 standard. the analysis results show that under normal conditions, the battery is capable of supplying power for 1.89 hours, but when considering 80% usage efficiency, the actual duration becomes 1.51 hours. in emergency conditions, the actual power supply duration is 1.27 hours, which still meets the edg activation time requirement (5–10 minutes, maximum 30 minutes). based on a comparison with the ieee 485-2020 standard, the battery capacity design has a sufficient safety margin. according to the latest maintenance evaluation, all parameters such as cell voltage, electrolyte specific gravity, and internal resistance remain within safe limits. the average effective capacity is still above 90%, and the electrolyte specific gravity has been temperature-corrected and complies with operational standards. nevertheless, the battery\\\'s age—exceeding six years—requires special attention due to the potential for future performance degradation.