In very simple terms a capacitor is just a storage of electrical charges. These charges stored by capacitor has to be supplied by some active source. Whereas a battery is a generator of electrical charges . In battery the charges are separated or generator by typically a chemical reaction . Of course the charge separation in battery can also be done by some other means like in solar power battery . Thus a battery is a energy conversion device which converts energy in one form ( e.g. chemical energy or solar energy ) into energy in another form i.e. electrical energy . Of course , having stored energy in capacitor it can be used for variety of purposes . Typically the amount of energy that you can store in a capacitor is limited but in batteries since the charge separation is continuously done much more energy can be generated. In fact in solar batteries , elctrical power can be generated as long as light is available. Typically in capacitors the unlike charges are stored separated by a dielectric ( insulator)- positive charge on one side and negative on the other. The separation generates an electric field in between which is where the energy is stored. Discharging the charges through another device gives back this stored energy .

In batteries where chemical reaction is source of energy , electrical energy is generated by oxidation ( electron donation by species ) and reduction reactions ( electron acceptance) . Thes two reactions occur at two electrodes ( called anode and cathode respectively). The driving force is the difference in Gibb's free energy . So long as this diffrence in Gibb's energy exists , battery can provide electrical power. Naturally when the chemicals deplete , the diffrence in free energy decreases and the battery dies down

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In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. If you have read How Batteries Work, then you know that a battery has two terminals. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.

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(Rated by 1 Council Member)