Bio-batteries are energy storage devices powered by organic compounds like glucose. They contain basic battery components - anode, cathode, separator and electrolyte. Glucose obtained through enzymatic hydrolysis of cellulosic materials provides the energy. The process involves cellulose breaking down into glucose and further into gluconolactone, protons and electrons. Bio-batteries have advantages like being instant recharging, non-flammable, non-toxic and providing a renewable power source. They have potential future applications as alternative energy sources and in medicine.