Smartphones and tablets these days are effectively pocket computers. But being multi-talented comes at a cost of considerable battery drain. Until the next battery breakthrough, most people today opt to carry an external battery pack (a.k.a. power bank) with them. Here are some tips on how to go about choosing one; or, to put it in another way, reasons why some battery packs are more expensive than others.
1. Capacity vs portability
The main spec to look out for in a portable battery pack is capacity, which is measured in milliampere-hour (mAh). The capacity of your device's battery is also measured in mAh, so loosely speaking, if your phone has a 2,000mAh battery, a 2,000mAh battery pack is able to recharge it fully once.
However, because of power lost due to voltage conversion and circuit resistance, and sometimes, the quality of the charging cable, this is rarely the case in reality.
While you can get one with a higher capacity (there are battery packs which go up to 20,000mAh) so that it's able to recharge a device multiple times over, keep in mind that this usually also means that it's bigger, heavier, and pricier.
Do you have a phone that supports Qi wireless charging? The Ark from Bezalel (who is now raising funds for it on Kickstarter) is a portable wireless charger with a 5,200mAh battery. Is this the future of external battery packs?
Above: This US$80 Anker Astro Pro2 has 'smart' ports that regulate the currents automatically. It's also one of the few battery packs with a multi-voltage port for 9V or 12V devices (like some ASUS and Acer tablets).
2. Your mobile device's input current
Most smartphone-oriented battery packs output at most 1A (at 5V) over the USB port. While this works fine for most people, some may notice that their smartphone now takes a longer time to recharge as compared to when a wall charger is used. This is especially true if the phone is able to accept a higher current.
Many recent Android smartphones have a 1.5A charging interface, and those which support Qualcomm's Quick Charge 2.0 standard (e.g. LG G2) can draw as much as 2A. So, manage your expectations.
Most tablets require at least 1A to charge too, with some drawing up to 2.5A.
Take the Apple iPad Air for example, which comes with a 12W USB wall adapter that provides 2.4A. If you were to plug the iPad Air to a battery pack's 1A USB port, it'll either not charge or charge super slowly.
So if you're looking to charge a tablet, our advice is to buy a battery pack that's capable of outputting higher than 1A (at least 1.5A if you've an Android tablet, and 2.1A if you've an iPad). Lastly, there's no harm using a higher-powered port on a smartphone, as the device only draws what is required. In fact, it may even charge faster if it's able to draw more.