Power banks are commonplace and with our increasing use of battery powered equipment: everything from mobile phones to battery powered headphones, portable speakers, MP3 players can be charged via a power bank. They are effectively a portable charger. All they need is a USB charging interface.
Power banks can be defined as portable batteries that use circuitry to control any power in and power out. They can charged up using a USB charger when power is available, and then used to charge battery powered items like mobile phones and a host of other devices that would normally use a USB charger.
There are a few different types of power bank portable charger that can be bought. Obviously the size is one of the main criteria, but there are some other categories that can be considered.
Universal or standard power bank: These are the normal power bank portable chargers which are available in the stores and online. They are charged from the normal USB sources like USB chargers.
Solar power bank: As the name indicates, these solar power banks can use sunlight to charge up. To do this they have photovoltaic panels. These are really only able to trickle-charge the internal battery when placed in sunlight because the solar cells are relatively small, but nevertheless this can be a very useful function.
There are two main forms of lifetime that are associated with power banks.
Charge discharge cycles: Any rechargeable battery will gradually wear out. Normally the lifetime of a battery is quoted in terms of the number of charge discharge cycles it can undergo before its performance falls by a given degree. Some cheaper power banks may only have a life of 500 or so charge discharge cycles, but better ones will have lifetimes of many more charge discharge cycles.
Self discharge time: All battery cells, whether rechargeable or primary have a certain level of self discharge. For rechargeable batteries these days with their own control circuitry, a small amount of power is required to keep these circuits alive. As a result there is only a finite time that a battery will remain charged.
A good power bank can hold charge for up to 6 months with only a small loss of charge, but lower quality ones may only retain a useful charge for about a month. These figures are for room temperature, but storing them outside these temperatures considerably reduces their performance.
All power banks use rechargeable batteries based around lithium technology. Lithium-Ion and Lithium-Polymer batteries are most commonly used for power banks but don’t be surprised if other types start to hit the market before long. Battery technology is key to many new developments: everything from mobile phones to electric vehicles, and as a result it is quite likely there will be some spin-offs into power banks.
The two technologies that are currently used have slightly different properties:
Lithium-ion: Lithium-Ion batteries have a higher energy density, i.e. they can store more electrical charge in a given size or volume, and are cheaper to manufacture, but they can have issues with ageing.
Lithium-polymer : Lithium-polymer power banks do not suffer from ageing to the same extent so are a better choice. However they are more costly to manufacture and as a result they may not suit all budgets. Sometimes it may be that it is best to spend less, especially if they are likely to be accidentally lost or left in places.
Power bank portable chargers are particularly useful as they enable battery powered items to be charged on the go. As it is not always possible to reach a mains power point every time a mobile phone or other battery powered item needs charging, these power banks are have now become an established product and they are very useful, especially when travelling.