Present rechargeable battery systems can be classified into two groups those employing liquid electrolytes and those employing solid electrolytes. Liquid electrolyte systems have been around for many decades and are the most well known to the general public. Examples of liquid electrolyte rechargeable battery systems include lead-acid, nickel cadmium, and nickel-metal hydride systems. Aqueous rechargeable battery systems have been used commercially for decades. Typical commercial examples of these battery types are lead-acid, nickel cadmium, and nickel metal hydride cells and commercial lithium batteries. Lead-acid batteries have been employed for some time for a variety of applications requiring general purpose electrochemical storage. The advantages of lead-acid batteries include low cost of manufacture, simplicity of design, reliability and relative safety when compared to other electrochemical systems. Relatively good specific power has enabled the widespread use of lead-acid batteries for starting, lighting and ignition (SLI) purposes for automotive, marine and aviation, applications. The lead-acid system has also found widespread use as traction batteries such as in golf carts and boats. In liquid electrolyte batteries, the electrolyte provides for ion transport between the cathode and anode. Typically, the amount of energy stored and retrievable from a conventional electrolyte battery is directly proportional to battery size and weight. A nickel-metal hydride rechargeable battery is an alkaline rechargeable battery. It include positive electrode plates having nickel hydroxide as its active material, negative electrode plates having hydrogen-absorption alloy, and separators interposed therebetween, has been known and widely used. For the nickel-metalhydride rechargeable battery, although it is inferior to the rechargeable lithium battery in terms of being relatively heavier, it has advantages in that it can be relatively easily produced at a reduced production cost in comparison with the rechargeable lithium battery. In view of this, nickel-metalhydride rechargeable batteries have been often using as power sources of portable instruments. Typically, aqueous battery products share several advantages over non-aqueous battery products. Being water based, the contents of the battery generally cannot ignite and burn. Thus, in abuse situations, aqueous batteries offer a relatively low risk of fire. Aqueous electrolytes have ionic conductivities that are typically from 2 to 3 orders of magnitude greater than those of non-aqueous electrolytes at a given temperature. Moreover, aqueous electrolytes are generally preferred over non-aqueous electrolytes from an environmental viewpoint. However, since liquid electrolytes are employed in these batteries, their operating temperatures are generally limited by the freezing point and boiling point of the liquid electrolyte and they are unsuitable for applications in severe environments such as desert or artic climates, deep sea, high altitude or space applications. Additionally, the corrosive liquid electrolytes employed by these batteries require complex packaging and sealing which add dead weight and dead volume. While polymer electrolyte batteries offer improvements over conventional liquid electrolyte batteries due to weight and size reductions which result in reduction of dead weight and volume, these batteries generally exhibit similar corrosion problems as liquid electrolyte batteries where the corrosive electrolytes which are employed react with anodes and cathodes and lead to rapid degradation of battery charging performance, reversible charge capacity and charge cycle lifetime.

More recently, advances in anode, cathode, and electrolyte materials and materials fabrication methods have led to the development of polymer electrolyte batteries and solid-state electrolyte batteries. The nonaqueous rechargeable battery is advantageous over the other rechargeable batteries in that it implements a high voltage between battery terminals for a single battery or cell, a high capacity, and a high output. Solid-state electrolyte batteries, or non-aqueous batteries, have the advantage that they are not limited by the electrochemical stability of a water based electrolyte. Thus, these batteries may operate at relatively high cell voltages, resulting in batteries with high energy densities. The solid electrolyte devices have the capability of pressure-packaging or hard encapsulation to yield extremely rugged assemblies. Solid-state batteries are capable of operating in temperature ranges which extend beyond either the freezing point or boiling point of a liquid electrolyte. Such non-aqueous batteries have the extension of the operating temperature range since the freezing and/or boiling-off of the liquid phase, which drastically affect the device performance when employing liquid electrolytes are no longer a consideration. For this reason, solid-state electrolyte batteries are particularly useful in severe environment applications in space, high altitudes, deep sea, desert or arctic climates. Solid electrolyte batteries are truly leak-proof, they have long shelf life due to the prevention of the corrosion of electrodes and of loss of solvent by drying out which occur when using liquid electrolytes. Since no corrosive electrolyte materials are employed, corrosion problems are eliminated and simplified packaging and sealing of battery cells is possible, eliminating unnecessary dead weight and volume. Due to the elimination of corrosion problems by employing solid-state electrolytes, electrolyte reactions with anodes and cathodes are eliminated resulting in stable charge capacities, high reversible charge capacity after extended cycling, and long battery lifetimes. Solid electrolytes permit micro-miniaturization, and they do not require heavy, rigid battery cases which are essentially "dead weight" because they provide no additional capacity to the battery but must be included in the total weight thereof. With the rapid advancement of small, lightweight and wireless electronic devices such as cell phones, camcorders, notebook computers and digital cameras, high-energy density solid secondary batteries are under vigorous development as power sources for such devices. Clean nonaqueous batteries, such as nickel-hydrogen or lithium batteries, have been attracting attention as batteries meeting the demand, taking the place of lead or nickel-cadmium batteries from the viewpoint of power saving and environmental conservation. In particular, lithium ion secondary batteries have been gaining weight from their lightness and high voltage and been put to practical use.

Rechargeable lithium batteries produce electric energy by an oxidation and reduction reaction during the intercalation and deintercalation of lithium ions. Lithium is highly desirable as the active materials for the anode and cathode, respectively, of rechargeable or secondary battery cells because they have the highest energy density on a weight or volume basis of any of the known combinations of active materials. A rechargeable lithium battery is considered to be one of the essential components in the digital generation since it is an indispensable energy source for portable digital devices. A rechargeable lithium battery uses materials from or into which lithium ions are deintercalated or intercalated for positive and negative active materials. A rechargeable lithium battery produces electric energy as a result of changes in the chemical potentials of the active materials during the intercalation and deintercalation reactions of the lithium ions. Rechargeable lithium batteries can be classified into two categories, namely a lithium ion battery or a lithium ion polymer battery. The lithium ion polymer battery uses a solid electrolyte such as a polymer, whereas the lithium ion battery that uses a liquid electrolyte. A lithium ion battery is a nonaqueous rechargeable battery using an organic solvent of lithium salt as an electrolyte. This kind of battery generates an electromotive force based on oxidation reduction derived from the migration of lithium ions. The lithium polymer batteries are divided into solid polymer lithium batteries, which do not contain liquid organic electrolytes, and gel polymer lithium batteries, which contain liquid organic electrolytes, according to the kind of electrolyte used. Lithium secondary batteries using polymer electrolytes are free from damage of devices due to leakage of electrolytic solution. Since electrolytes of lithium secondary batteries serve as separators, batteries can be made smaller. The lithium ion polymer battery, therefore, is lighter and has a smaller volume than the lithium ion battery. The lithium ion polymer battery is capable of being fabricated into various shapes. Rechargeable lithium batteries are often utilized in applications where high energy density is a requirement. A lithium battery may contain one lithium electrochemical cell, but more commonly it consists of several lithium electrochemical cells in series or parallel, or a combination of such connections.

Rechargeable batteries are capable of being charged prior to initial use and recharged after being discharged. Generally, rechargeable batteries are charged by a battery charger having a power supply that can provide a supply of DC current. A rechargeable battery accepts the electrical current and converts it into chemical energy. Rechargeable batteries are oftentimes packed together in series as a rechargeable battery pack to provide a desired operational voltage and current. The typical battery pack charger has open faced surfaces to couple with the rechargeable battery pack. The battery pack charger includes two opposing surfaces one having a positive electrical contact protruding through it and another having a negative electrical contact protruding through it. A rechargeable battery can be charged at higher rates provided that safety precautions are taken to prevent overheating of the battery thereby preventing a possible fire or damage to the battery or the battery charger. Rechargeable batteries are provided with a variety of protective functions for preventing damage to the battery caused by abnormal use such as overcharging, overdischarging, or short-circuiting. Such battery protection circuit is generally unitized with the battery as part of battery pack configuration, in which a circuit board that makes up the battery protection circuit is integrally contained in the pack case along with the lithium ion rechargeable battery. In addition to preventing overcharging and over discharging as mentioned above, this battery protection circuit can also have such functions as cutting off excessive current or monitoring cell temperature. Rechargeable batteries should be charged using the appropriate charging method in order that they may be used to their full extent. For example, the NiCd battery is preferred to be fully discharged periodically. The Li-ion battery is preferred to be charged before it is discharged up to the discharge terminal voltage. The lithium polymer battery should be always in a charged state before it is exhausted by discharge. The durability of the lithium polymer type could be shortened, if it is fully discharged like nickel cadmium battery.