: 190
Primary batteries (non-rechargeable): Leclanche dry cell (Zn/MnO2, 1.5 V, common flashlight battery), Mercury cell (Zn/HgO, 1.35 V, constant voltage, hearing aids). Secondary batteries (rechargeable): Lead-acid (Pb/PbO2/H2SO4, 2V per cell, 12V car battery — H2SO4 consumed during discharge, regenerated during charging), Ni-Cd (Cd/NiOOH/KOH, rechargeable, portable devices), Li-ion (LiCoO2/graphite, 3.6V, highest energy density, phones/laptops). Fuel cells (continuous fuel supply): H2-O2 fuel cell (2H2 + O2 -> 2H2O, ~1V, zero pollution, high efficiency up to 70-80%, used in spacecraft). Key advantage of fuel cells: direct chemical-to-electrical conversion bypasses Carnot efficiency limit. No moving parts, low maintenance, clean operation. Disadvantage: expensive catalysts (Pt), hydrogen storage challenges.