<P> Since the Universal Serial Bus specification provides for a five - volt power supply, it is possible to use a USB cable to connect a device to a power supply . Products based on this approach include chargers for cellular phones, portable digital audio players, and tablet computers . They may be fully compliant USB peripheral devices adhering to USB power discipline, or uncontrolled in the manner of USB decorations . </P> <P> Although portable solar chargers obtain energy from the sun only, they still can (depending on the technology) be used in low light (i.e. cloudy) applications . Portable solar chargers are typically used for trickle charging, although some solar chargers (depending on the wattage), can completely recharge batteries . Other devices may exist, which combine this with other sources of energy for added recharging efficacy . </P> <P> Powerbanks are popular for charging smartphones and mobile tablet devices . A powerbank is a portable device that can supply power from its built - in batteries through a USB port . They usually recharge with USB power supply . Technically, a powerbank consists of rechargeable Lithium - ion or Lithium - Polymer batteries installed in a protective casing, guided by a printed circuit board (PCB) which provides various protective and safety measures . Due to its general purpose, powerbanks are also gaining popularity as a branding and promotional tool . Different brands and promotional companies use it as a promotional tool and provide a customized product . </P> <Ul> <Li> Capacity in Wh: Total power capacity measured by multiplying mAh by voltage . </Li> <Li> Capacity in mAh: mAh stands for milli Ampere - hour and measures the amount of power flow that can be supplied by a certain powerbank at a specific voltage . Many manufacturers rate their products at 3.7 V, the voltage of cell (s) inside . Since USB outputs at 5 V, calculations at this voltage will yield a lower mAh number . For example, a battery pack advertised with a 3000 mAh capacity (at 3.7 V) will produce 2220 mAh at 5 V. Power losses due to efficiency of the charging circuitry also occur . </Li> <Li> Simultaneous charging and discharging: need to specify if the powerbank can be used while it is charging . </Li> <Li> Number of output USB ports: This specifies the number of devices that can be charged simultaneously . </Li> <Li> Output current rating: This specifies the current rating that it can charge maximum . The higher the number, the better the powerbank . This can vary from output port to output port . </Li> <Li> Input Current Rating: Input current rating is the amount of current the powerbank is able to draw at its maximum level while getting charged . </Li> <Li> Safety Protections: Over Voltage Protection, Over Charge Protections, Over Current Protections, Over Heat Protections, Short - Circuit Protections and Over Discharge Protections are the common safety measures observed with standard powerbanks . </Li> <Li> LED Indications: The Led glows as per indicating the amount of charging ability left with the powerbank . </Li> </Ul>

What is the use of power bank charger