A battery is an electrochemical cell (or enclosed and protected material) that can be charged electrically to provide a static potential for power or released electrical charge when needed. Without a battery, mobile phones don't start to work, not even for other operations.
smart phone's battery
Phone Battery Voltage

    Depending on the design and chemistry of your battery, you may see the mobile phone battery sold under different nominal "voltages".

    There are two kinds of most common voltages:

  • 3.7V- 4.2V: Almost all lithium polymer batteries are 3.7V or 4.2V batteries. What this means is that the maximum voltage of the cell is 4.2v and that the "nominal" (average) voltage is 3.7V. As the battery is used, the voltage will drop lower and lower until the minimum which is around 3.0V. You should see the number 3.7V written on the battery itself somewhere.
  • 3.8V- 4.35V: This is the latest chemistry, and it has a little more power as indicated by the voltage being higher than 4.2V.
mAh (Milliamp Hours)
    A unit for measuring electric power over time. mAh is commonly used to describe the total amount of energy a battery can store at one time. A battery rated for more mAh will power a phone for a longer amount of time, given the same usage pattern. the trade-off is that batteries with more mAh are generally also physically larger and heavier. More technically, a higher mAh rating means the (fully-charged) battery can power a device that consumes more power and/or for longer amount of time before becoming depleted and needing to
Battery Types
  • Li-Polymer (Lithium polymer): A batter technology similar to lithium-ion Current "lithium-polymer" batteries are technically "lithium ion polymer" since pure lithium-polymer batteries are not yet commercially viable. pure lithium- polymer batteries, once available, will theoretically provide considerable benefits over current battery technologies.
  • li-lon (lithium lon): refers to the lithium-lon type of battery, often used to power wireless communication devices. li-lon batteries are lighter weight than earlier battery types, have a relatively long cycle life, and generally do not suffer from "memory" effect.