The rapid electrification of public transportation in India represents a critical transition toward sustainable mobility, reduced greenhouse gas emissions, and improved urban air quality. Electric buses (E-buses) are emerging as a key component of this transformation; however, their long-term technical reliability, battery degradation behaviour, and lifecycle performance under Indian operating conditions remain insufficiently understood. This research presents a comprehensive multi-scale analysis of electric bus systems, focusing on battery degradation modelling, mechanical reliability assessment, seasonal performance variation, and lifecycle optimization within the Indian context. The study investigates lithium-ion battery chemistries commonly used in Indian electric buses, including Lithium Iron Phosphate (LFP) and Nickel Manganese Cobalt (NMC), with emphasis on depth of discharge (DoD), C-rate effects, equivalent full cycle (EFC) counting, and thermal stress impacts. A predictive degradation framework is developed to estimate state of health (SoH) under variable duty cycles and climatic conditions. Results indicate that temperature variations above 35°C and high C-rate charging significantly accelerate capacity fade and internal resistance growth, directly influencing operational range and battery lifespan. Mechanical reliability analysis is conducted through Failure Mode and Effects Analysis (FMEA) and stress evaluation of suspension, axle, braking, and chassis systems. The increased vehicle mass due to battery integration is shown to elevate suspension and structural fatigue risks compared to conventional diesel buses. Seasonal performance evaluation highlights summer-induced thermal derating, monsoon-related electrical ingress risks, and winter-associated capacity reduction. A techno-economic assessment incorporating total cost of ownership (TCO) and lifecycle cost modelling demonstrates that despite higher initial acquisition costs, optimized charging strategies, predictive maintenance, and trained driver intervention significantly improve economic viability. The research further integrates preventive maintenance frameworks, telematics-based diagnostics, and driver training impacts on energy efficiency. The findings contribute to the development of a predictive reliability and lifecycle optimization framework tailored to Indian operating environments. This study provides actionable insights for policymakers, fleet operators, and manufacturers to enhance electric bus deployment strategies, improve battery longevity, and ensure sustainable public transportation systems.