An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its negative terminal is the anode. The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal. When a battery is connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically the term "battery" specifically referred to a device composed of multiple cells; however, the usage has evolved to include devices composed of a single cell.

विद्युत कोष (Battery) विद्युत ऊर्जा का स्रोत है जिसे रासायनिक उर्जा से प्राप्त किया जाता है। वैद्युत अभियांत्रिकी एवं इलेक्ट्रानिकी में दो या दो से अधिक विद्युतरासायनिक सेलों के संयोजन को विद्युत कोष कहते हैं। ये रासायनिक उर्जा भण्डारित करते हैं एवं इस उर्जा को विद्युत उर्जा के रूप में उपलब्ध करते हैं।