The main function of a power bank is to charge your portable electronics, including smartphones, tablets, digital cameras etc. without connecting it to a power outlet such as AC socket. If you're like me, you probably found yourself at least once in a situation when you run out of battery juice in your smartphone and desperately look for a way to recharge it. A charged power bank can be very convenient in such times, it also gives you peace of mind. Even if you are not low on battery, you migh use your power bank to help someone else out.
Power banks are also called battery packs, external batteries, portable chargers, fuel banks, and they come in various shapes and sizes. There are small ones, which will recharge your smartphone once or twice, medium ones that can be used to recharge your tablet's battery or your smartphone many times, and the bigger units with multiple outlets that can also recharge your laptop on the go.
The battery is the most important element of the power bank, and its size is usually rated in miliamp-hours (mAh). The typical ranges available are between 2,000mAh available in pocket-size units up to 50,000mAh that can are more suited to carry in your bag or backpack.
Here is what charging performance you can expect from different battery sizes:
2,000mAh - recharge your smartphone in emergency (maximum once)
5,000mAh - charge a smartphone up to 3 times, and a tablet 1 - 1.5x
10,000mAh - multiple smartphone charges (4 - 8 times), tablet 2 - 3x
50,000mAh - mulitple smartphone/tablet charges, recharge your laptop
Most power banks come equipped with USB ports, which can be used to charge most portable devices today. It is important to understand that USB ports deliver different power output, most commonly 0.5Amp, 1Amp or 2.1Amp. The higher the Amp output in the USB port, the faster it can charge your smartphone (up to a limit).
When your power bank has more than one USB port, things get a bit more interesting. Depending whether you are charging only one device or two at the same time, the charging speed could be different. That is why you should be looking not only at how many Amps of output the single USB port has. You should also check how many Amps in total the power bank can deliver.
For example, if you have 2 USB ports in your power bank, one rated at 2.1Amp and the second at 1Amp, with total output 2.1Amp, you will be able to charge your smartphone at optimum speed only if there are no other devices being charged at the same time. If you connect another smartphone, both of them will be charged at around 1Amp, which will take longer.
Your power bank will usually include a charging cable, typically a USB or micro-USB cable, which you will connect to USB wall charger or another charging device, such as laptop. The accepted power input is also measured in Amps, and the higher the input Amps, the faster the power bank will recharge (this also depends on the power output supplied by your USB wall charger).
Below we listed some of the most popular power banks available today: