Typically, cell phones employ rechargeable batteries, such as NiMH batteries, Li-ion batteries, or Li-polymer batteries, as power supplies. Rechargeable batteries have gained wide acceptance and usage as power sources for portable appliances. Mobile communications devices, entertainment devices, and video devices are just a few of the many appliances now using rechargeable battery technology. The difference between using lithium batteries and using of the common nickel cadmium or nickel hydrogen batteries for the storage battery resides in high electric capacitance of the lithium batteries, and the available hours of use of lithium batteries when they are charged in saturation which are at least triple in amount more than that of common batteries. A lithium ion battery is characterized by its anode and cathode active materials made of a substance capable of occluding and releasing lithium ions. In principle, it works without requiring electrode position of lithium metal. Its anode and cathode may be made of a variety of substances capable of occluding and releasing lithium ions. 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. These rechargeable lithium batteries have been evaluated as being superior to the nickel-metalhydride rechargeable battery particularly in a viewpoint that they are expected to have a relatively higher energy density.

Lithium-based battery cells are an attractive energy source for portable applications, due in part to their ability to provide relatively high energies and long cycle life. Lithium ion secondary batteries are small and lightweight, and can be charged and discharged more than 300 cycles repeatedly, and are hence used widely in laptop computers, cellular phones and many other electronic appliances, and the demand is increasing. Lithium is the lightest of all the metals, with a high electrochemical potential, thus providing high energy densities. Rechargeable batteries using lithium as the electrochemical material are capable of providing higher energy to weight ratios than those using other chemistries. The lithium secondary batteries are classified into lithium metal batteries using liquid electrolytes, lithium ion batteries and lithium polymer batteries using solid-state polymer electrolytes. 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 batteries that are widely being used as power supplies for portable electronic devices such as notebook computers, camcorders or mobile phones, include a cathode containing a lithium metal composite oxide or sulfur capable of intercalating and deintercalating lithium ions, an anode containing a carbon material or lithium metal, and an electrolytic solution having an appropriate amount of a lithium salt dissolved in a non-aqueous mixed solvent. Lithium secondary batteries using polymer electrolytes are free from damage of devices due to leakage of electrolytic solution. Also, since electrolytes of lithium secondary batteries serve as separators, batteries can be made smaller. Also, high-energy density lithium secondary batteries can be used as very convenient power sources. Owing to these advantages, much attention is being paid to the lithium secondary batteries as power sources or memory backup sources for portable electronic devices.

The power source of the mobile phone generally comes from a rechargeable battery, therefore charging efficiency and the durability of the battery are important issues. A cellular phone is provided with a rechargeable battery pack which is easily detachable from the cellular phone for charging when the battery pack's power is exhausted. Various types of rechargeable battery packs are known for use with cellular phones. The vast majority of such battery packs use either lithium cells, or nickel-cadmium or nickel-metal hydride cells. Specifically, lithium-base rechargeable batteries are suitably used. The cell phone rechargeable battery generally has a rectangular configuration having a predetermined thickness. Generally, the positive electrode is provided as a projection formed centrally on one of longitudinally opposite end surfaces of the battery, whereas the negative electrode comprises the entire conductor surface of the battery except the positive electrode. When a battery runs out of electricity, the rechargeable battery is often removed from the housing of the mobile phone so that the battery can be recharged or replaced. Generally, a battery charger for a cellular phone charges a battery through a connection terminal at the rear of the battery in a state that the battery is only inserted into the battery charger or the cellular phone having the battery is inserted into the battery charger. The mobile phone battery charger for the mobile phone is connected with a long power cord with an electric plug.

Cell phones are needed to perform a variety of functions to enable mobile professionals to stay current with information and communications, such as e-mail, corporate data and organizer information. As electronic components decrease in size, the shape and size of a portable phone is less a factor of the cell phones. The demand for mobile phones of smaller size and increasingly attractive appearance rapidly increases. Accordingly the battery pack powering a cell phone is required be made small and compact to achieve an overall lightweight device. It is also important that the handheld device be supplied with the correct battery pack for optimal performance and to prevent damage through a physical and/or electrical mismatch. Furthermore, a battery pack needs to be properly mountable for secure placement, easy removal, and reliable contact between the battery pack power and data terminals and the handheld mobile communication device contacts. Moreover, a circuit for monitoring battery temperatures and measuring battery remaining capacity is an essential mechanism when a rechargeable battery is used as power source for portable information equipment. Recently mobile phones have become one of the most widely used and convenient communication equipment. A connection mechanism, therefore, is required for connecting the rechargeable battery to the housing of the mobile phone and for releasing the rechargeable battery from the mobile phone at appropriate times. It is also desirable for a cell phone user to know the operational time remaining with an installed battery so as to be able to properly plan for future usage of the device, and to generally know when the battery should be recharged.

Cellular phones typically have an outer casing in which the main circuit board and other components are mounted. The outer casing has a recess on one face for removably receiving a battery unit enclosed in a battery housing with contacts on the outside of the battery housing for engaging contacts on the recessed face of the phone casing. Typical battery housings for cellular phones incorporate a plastic case or enclosure for holding the battery cells and often other electrical circuitry components necessary to build-up the complete battery structure to power the phone when the battery housing is engaged with the cellular phone. A battery latch assembly is used to hold the battery pack to the phone housing. The battery pack must be securely attached to the phone housing so that a secure electrical contact is formed between the battery supply and the phone's electrical circuitry. The battery pack is locked by a locking apparatus mounted on the body of the mobile phone, and at least one guide rib is formed on the body to guide the battery pack. A battery connector used in a mobile phone typically comprises resilient electrical terminals that protrude beyond a mating face of a housing of the connector within which they are mounted. These terminals are biased into the housing when a battery is mounted in the apparatus and electrically connecting with the battery connector. A mobile phone generally presents to the user a graphical indication of the state of the battery charge level: for example, there could be an image of a battery, divided into several segments. When no segments are permanently displayed, then the battery is low. When all segments are displayed, the battery is full.

In general, a mobile terminal such as a mobile telephone has a battery pack detachably mounted on the rear side of its body as a power source. The battery pack has electrodes formed on the inner and outer surfaces of its lower portion. The electrodes formed on the inner surface of the battery pack are so structured as to contact the connection terminals formed on the rear surface of the body of the mobile telephone. The electrodes formed on the outer surface of the battery pack are so structured as to contact the connection terminals of a charger during charge. In order to connect the battery pack and the phone electrically, contact pins to be contacted with an electrode of the battery pack are provided in the phone. Battery packs for use with cellular phones normally employ a plurality of battery cells generally comprised of lithium metal or nickel metal hydride material. They are different in battery characteristics such as capacity, discharge characteristic, and necessary charging period from each other. Battery packs containing nickel-based cells generally contain the number of cells required to provide the operating voltage for the equipment, and there is therefore no necessity for voltage conversion circuits, but only for over-temperature and short-circuit current protection circuits. In battery packs containing lithium cells, voltage conversion and control circuitry are not usually incorporated. However, lithium cell battery packs must include voltage and current protection devices in addition to the standard components contained in nickel-based cells.

A battery pack for use as a rechargeable power source of portable terminal equipment such as a cellular phone is provided with a protective circuit for preventing a rechargeable battery from overcharge, overdischarge, or overcurrent. The protective functions are necessary because the battery cell, such as a lithium ion battery cell, cannot by itself provide these functional safety requirements without the protection circuits. Over charging and over discharging of the battery cells can reduce the lifetime, or the performance or even destroy the battery. The voltage control and protective circuitry ensures correct charging and discharging conditions to permit proper operation of the battery in conjunction with the electronic equipment. The battery control circuit measures the charging current (CC), the charging voltage (CV), the discharging current (DC), and the discharging voltage (DV). 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. The protection circuit functions to protect not only the user, but also the battery cell and the mobile phone from damage in the event of misuse or a malfunction. Generally, the protection circuit electronic components are mounted on a printed circuit board of some type which is also contained within the battery pack.