Portability

• The primary function of a battery is to provide power for portable devices like cellphones, laptops and GPS systems. With batteries, there is no need for a wire to connect the device to the power grid. Often, these batteries are rechargeable, so the battery functions as an energy storage device as much as a power source.
  
  

Tempory Power

• Many consumers of public utility power, such as hospitals, cannot tolerate power interruptions. When power from the public utility source is lost, as in a hurricane or earthquake, there is an automatic switch to a backup power generator. This transaction cannot be instantaneous because the generator must be turned on and warm up before it can be brought up to full operation. A set of batteries prevent a power loss during this transition time. When the generator starts supplying full power, some of the generator output is tapped off to recharge the batteries. These batteries will have to fill in during future times when the generator must be stopped, such as when the fuel tanks are refilled.
  
  

Power Collector

• Many environmentally friendly power sources produce power based of the actions of the natural world. Solar power is only generated during the day and is interrupted during rainstorms or even when a cloud passes overhead. Wind turbines operate whenever the wind is blowing. The requirement for power usage is independent of power generation. People will use lights and appliances regardless of when the power was generated. To collect the power during generation and dispense it as needed, power sources recharge batteries for later consumer use.
  
  

Clocks and Emergency Equipment

• Some devices must maintain a minimum amount of electrical activity, even when the main power is turned off. One of the most common of these situations is the clocks in cars and computers. Even when the power is off, the clock must keep recording the passage of time. Otherwise, the clock will have the wrong time when the system starts up every morning. Batteries are also an important part of backup systems that trigger alarms that go off and provide emergency lighting when the power goes out.