Batteries for the cell phones are available and there are different reasons to purchase. If your battery is not holding a charge and dies much sooner than it did when new, it is time to get a replacement. If you are using your cell phone all day and need the continuous operation then a spare charged battery can be swapped quickly and keep using the cell phone. There are both desk and automobile chargers available to charge a battery without the phone. Batteries very in price, size, shape, and material they are made of. The material is the biggest variable in the length of time your phone will work on a single charge. The material also will change the cost of the battery. Batteries are basically made to meet a certain voltage, Ah, and physical size. Here is a description of the different types of rechargeable batteries you may find in cell phones. Lithium Ion (Li Ion): One of the newer rechargeable battery technologies, Li Ion batteries can deliver 40% more capacity than comparably sized NiCd batteries and are one of the lightest rechargeable batteries available today. Li Ion batteries are the batteries of choice in notebook computers, wireless telephones and many camcorder models. They are also one of the more expensive rechargeable technologies. Nickel Metal Hydride (NiMH): Interchangeable with most NiCd batteries, nickel metal hydride (NiMH) batteries generally deliver 10-25% greater capacity than NiCds and are environmentally friendlier than NiCds since they do not contain cadmium. Used in many wireless phone and camcorder. Nickel Cadmium (NiCd): One of the most proven and widely used rechargeable batteries. Very dependable but contain cadmium and have relatively low capacity when compared to other rechargeable systems. Very good high rate discharge capabilities make them very popular in high drain applications such as power tools. These are not a good choice for the cell phones, any more, with the newer types available now.                   Capacity - The ampere is the measurement of current in the electrical circuit. The Volt is the pressure required to move the electrons in the circuit. If you compare it to a water hose, then the volt is the pressure behind the water and the ampere is the amount of water coming out of the hose or pipe. Battery storage capacity is measured in Ampere Hours, smaller battery capacity is measured in mAh or MilliAmp Hours. mAh: A 1/1000th of an amp-hour, e.g.: 1.0Ah = 1000mAh. The higher the Ah or mAH the more capacity to hold a charge. This translates into longer lasting battery, provided you have the same load on it. For the longest lasting get the one with the highest Ah on it. This will also mean a larger physical size many times, so be sure it will fit in the case. The size is the main limitation on the battery capacity, besides the material it is made of. You may not have a choice other than to replace with the original type and size of battery. Always charge the battery to full charge before using the first time. If the battery starts going dead faster try discharging till clear dead then do a full charge. This works better on the old NiCd batteries but will sometimes work on the newer types. Safety: If you replace your battery dispose of it properly. DO NOT burn or throw in the trash. Save the environment and recycle or dispose at sites that take that type of material. To reduce risk of fire or burns, do not disassemble, crush, short external contacts, or dispose of in fire or water. Emergency Cell Phone Chargers: There are several makes of emergency cell phone chargers available today. Some make use of AA or AAA batteries and others have a crank to provide the energy to recharge the cell phone battery. You just plug them into the phone and you can still use like you would if you were connected to a regular charger. These are handy to have when you get caught out and have no charger available or in emergency situations at home and the power is out and no communication but the cell phone. If the cell phone battery is dead, the emergency charges will get you back on the air to communicate and call for help or what is necessary.