Depending on the operational characteristics and the electrochemical system (a set of electrodes and electrolyte) used, chemical current sources (CCS) are divided into primary (not rechargeable, galvanic cells), which usually become out-of-use after they are fully discharged, and secondary (rechargeable, batteries), where the reagents are recovered when charging by passing current from an external source. Such a division is rather arbitrary, since some galvanic cells can be partially charged.

Chemical current sources consist of two electrodes: a cathode with an oxidant and an anode with a reducing agent, and they contact with an electrolyte. The electrode potential difference evolves, which is an electromotive force equal to the free energy of redox reactions. The operation of chemical current sources is based on the spatially separated processes with the closed external circuit: the reducing agent is oxidised at the cathode and the nascent free electrons generate the discharge current by moving in the external circuit to the anode, where they participate in the reduction reaction of the oxidant.

Currently, there are a lot of different types of CCSs: lithium-ion (Li-ion), lithium-polymer (Li-pol), nickel metal hydride (Ni-MH), nickel-cadmium (Ni-Cd), lead-acid, air-and-metal, etc., as well as a great number of primary CCSs, with salt, alkaline and lithium being the most popular. The most important and promising chemical current sources include fuel cells (electrochemical generators) capable of durable continuous operation with a constant supply of new portions of reagents to the electrodes and removal of reaction products.