What types of batteries are used in spacecraft and what are their characteristics?

Spacecraft batteries store energy for eclipse periods and peak loads. Types: Lithium-ion - High energy density (150-250 Wh/kg), most common for modern missions, 5-15 year life with proper management, sensitive to overcharge/overdischarge. Nickel-hydrogen (NiH2) - Lower energy density but extremely long cycle life (>50,000 cycles), used on ISS and older GEO satellites, pressure vessels required. Lithium-polymer - Very high energy density, good for short missions. Selection factors: Cycle life (LEO: 5000+ cycles/year, GEO: 90/year), Depth of discharge limits, Temperature range, Radiation tolerance, and Mission duration. Battery management: Cell balancing, Charge/discharge control, Temperature regulation, and State of health monitoring. Sizing accounts for degradation over mission life plus margin.