Wondering what a universal battery charger is?
A universal battery charger utilizes similar technology to the batteries found in most mobile devices and laptops. As with most modern batteries, external battery chargers utilize a lithium-ion battery pack. Lithium-ion battery packs vary greatly in shape and size, but are still comprised of the same main elements to give users the most efficient and safe charge. 



Below are the six components that form most lithium-ion battery packs:
Lithium-ion cells: The lithium-ion cells found in an external battery pack come in two main shapes, cylindrical and prismatic. Cylindrical lithium-ion cells resemble AA battery cells. Prismatic lithium-ion cells are generally square or rectangular.

In addition to the lithium-ion cells, external battery packs contain a computer, which is made up of:
Temperature sensors: The temperature sensors in lithium-ion battery packs monitor the battery temperature to ensure the battery does not overheat and damage the battery pack or the device connected to the pack charging. Depending on the size and capacity of the lithium-ion battery pack, it may contain one or multiple temperature sensors. In addition to monitoring the temperature, the computer employs automatic safeguards to protect your devices. Some of these safeguards may be that in the event the battery pack gets too hot during charging or use; the computer will shut down the flow of electricity to ensure it does not overheat. The computer may also stop the external battery pack from turning on if the battery pack becomes too hot from being left in sunlight for an extended period of time. These safeguards ensure that your devices are not damaged during the charging process and remain fully functional.
Shielded Notebook Connector: The shielded notebook connector component controls the flow of power and information into and out of the battery pack.
Voltage Converter and Regulator Circuit: The voltage converter and regulator circuit ensures that the lithium-ion battery pack maintains safe levels of voltage and current. This component is extremely important as it is a key safeguard to make sure that your device never experiences a power surge that could harm it.

Final conclusion：
You can charge multiple devices at once. Many external battery packs come equipped with multiple charging ports, which makes it possible to charge back up multiple devices at once. You will still need to have a charging cable to connect each device, unless you choose one with wireless charging capabilities, but you can continue on your way with your external battery pack adding juice back into all your most used devices without slowing your pace. In the new wave of wireless charging enabled devices, you can ditch the cables as long as the device you are trying to charge is enabled with wireless charging technology as well.