A Long-Term Service Agreement (LTSA) is a contractual arrangement between an asset owner and a service provider that ensures ongoing maintenance, operational support, and performance management over a defined multi-year period—typically between 5 and 20 years. In the context of Battery Energy Storage Systems (BESS), LTSAs cover preventative maintenance, spare parts supply, performance guarantees, remote monitoring, and corrective actions. These agreements are crucial for asset longevity, reducing operational risk, and stabilizing life-cycle costs. LTSAs often include key performance indicators, availability guarantees, and financial incentives tied to system uptime and performance targets.