What is a portable power bank?
By now you have likely heard of, and understand what a mobile power bank does. But in case you don't, here's the explanation. Effectively it's a high capacity battery (much higher than your mobile phone), which can be used to charge all sorts of devices from it.
How do I decide what's right for me?
Take a look at the different features below that cover the major differences.
Self-Contained Recharging
We carry several solar-recharged units. These are useful in emergency scenarios (i.e. the power is out due to storms), as well as camping and off-grid applications. They can still be recharged when mains power is availa-ble, but if you think you might need this feature they're a great option. Of course, they're not quite as compact as they need to make room for the solar panels.
Built-In Leads
If you're primarily only charging one type of device, then having built-in leads that suit your device will save you from having to carry an appropriate cable to use the USB ports. Of course, even the ones with leads have USB outlets for universal charging. However, the self-contained leads will mean there's one less thing to po-tentially leave behind, so you don't find yourself with a power bank but no charging lead.
Multiple Ports
It's always useful to be able to charge more than one unit at a time. While you'll have to share the overall charging capability between the two devices you're charging, it can come in handy.
Battery Status
Being able to find out how much charge your battery bank has left is very useful. Sometimes this will come in the form of a series of LEDs (i.e. 4 LEDs for fully charged, 1 LED for needs recharging, etc), whereas other units will have a full LCD with battery indicator. Ultimately they all work the same, but you may have an aes-thetic preference. Either will help you ensure you recharge the bank before you think you'll need it.
Capacity
This is perhaps the largest consideration of them all, or at least the most complex. Capacity basically refers to the amount of charge the power bank can hold. The more it can hold, the more times you can recharge your phone (or whatever you're charging) before the power bank itself will need a recharge. The maths is rather simple. The key is knowing what the capacity of your device is. You can usually find this information in the manufacturer's specifications or user manual. If you don't have those anywhere, a quick online search for your device such as "iPhone® 6 battery capacity" will yield a wealth of information for you to use. If you use Google, they're rather good at summarising this information for you so you don't even have to click through to a web-site. Once you've found that information, here's how to apply it. For this example, we'll use an iPhone® 6s. The iPhone® 6s has a capacity of 1,715mAh (milli ampere hour), This means that the battery can deliver 1,715mA (milli amps) of current for 1 hour at the battery's rated voltage. Precisely what that means doesn't really matter here, because you're comparing like terms. Therefore, if you take the mAh (milli ampere hour) rating of the power bank you're looking at, you can approximately work out how many recharges you'll get.
For example:
An iPhone® 6s with our 5,000mAh power bank:
5,000 / 1,715 = 2.92
For use with our 10,000mAh power bank:
10,000 / 1,715 = 5.83.
For this combination, you can theoretically get almost 3 recharges of your iPhone® from completely flat to fully charged. For the 10,000mAh model, it would be almost 6 charges.
A caveat... Now this maths is only theoretical and great for comparing devices. Whenever electrical energy is converted, stored, or discharged - there's always some element of waste. Whether it's wasted as heat or just the electrical circuit to make it all work, there's always some loss. One of the great technical challenges of the modern age is to eliminate this waste. Generally you'll get around 80-90% efficiency, but this will depend on the device, ambient temperature and a whole suite of factors outside of your control.
There you have it. Now you can make an informed decision on the size of battery bank and the features that you require!