USB battery - mobile power supply via USB charger
USB batteries have 1 or 2 standard USB ports with an output voltage of 5V. The power that is provided will vary depending on the terminal type, between 500mA and 2.5A, and is controlled via the connected device. A few devices have up to four outputs for the event that you wish to connect multiple devices simultaneously.
Devices that need a 5V power supply such as e.g. mobile phones, smartphones as well as digital cameras can be connected to the USB connecting cable of the device or to the connecting cable delivered with the USB battery with an adaptor.
The advantage of a USB rechargeable battery with 2 USB ports is that you can connect and charge 2 devices in parallel there.
USB rechargeable battery operation
Depending on the rechargeable USB battery the devices are charged immediately after connection or you can operate an ON/OFF switch whereby the charging process is started.
Charging a USB rechargeable battery
The rechargeable USB batteries are normally charged via micro USB port. However, a few power banks still have a mini USB or have a DC input for charging via a power supply unit.
- The micro USB input has the advantage, that there are many chargers on the market using a micro-USB connector. This adapter can then be inserted directly into this USB Charger input.
- A DC input has the beneit that these power banks are then charged with higher power capability. However, the disadvantage is that you have to take an additional charger.
The charging process is normally finished when the charging current falls under a certain pre-determined limit.
Practically all power banks have an LED display which indicates the state of charge. However it is important to note that most displays are based on the measurement of internal battery voltage and can therefore not be very accurate. During discharge the interal battery voltage drops more strongly at the beginning, which can cause an LED to go out fairly quickly. On the other hand it can take a considerably longer time until the next LED goes out. If the last of the available LEDs goes out then the power bank has discharged itself and shoudl be recharged as quickly as possible, at least partially.