Dude my battery is flat. Where is that power bank?

power bank

Everyone needs an emergency power bank. The challenge is to cut through the marketing hype of the plethora of brands and models.

The power bank challenge starts with the name itself. People call them a power thingy, battery pack, pocket power cell, portable battery charger, power bank, or even a fuel bank. They are all the same thing – a portable battery to recharge your device. Power in/power out!

You only need to be clear on two things.

First, the power capacity of the device you want to charge must be at least 20% less than the power bank capacity.

Second, don’t get caught in the marketing hype. They all work similarly. If you want to pay more for a prestige brand, diamantes or a faux leather case, then so be it.


Capacity is in milliamp hours ‘mAh’. Just like a petrol tank holds a certain number of litres it is just the electric power the battery can store.

Consumer grade power banks have a mAh rating between 2,000 mAh and 25,000 mAh at 5V.

To work out the required capacity, you need to understand the capacity of the batteries you are planning to charge. Either locate it on the device or check the internet for its mAh capacity.

The iPhone 8 has a battery capacity of 1821 mAh. To fully charge it you need a power bank that has a capacity of 2500 mAh or greater (about 20% of the electric power ‘evaporates’ through the charging process). If you power bank is 5,000mAh, it means you can recharge the iPhone twice!

For the technically oriented mAh = mWh/V. For example, if a Tablet has a 40Wh (40,000 mWh) at 5V capacity. 40,000 mWh / 5 V = 8,000 mAh

Weight, Size and Shape

The more mAh, the bigger and bulkier it is. Regardless of the brand, they are all similar weight and size for a given capacity. There are some small variances depending on the battery type used. The power bank can be cylindrical, square or slim.

A slim is best for shirt and jeans pockets. The Anker PowerCore Slim 5000 fits that purpose.

If you are looking to buy the smallest, lipstick size power bank, then consider the Jackery Force65

If weight is not an issue, then look at the 10-20,000mAh or larger and throw it in the backpack.

Recharge Time

Two factors determine how long it takes to recharge a battery. The USB charger’s amp rating and the battery capacity.

In theory, using a 5V USB charger, a 5,000mAh power bank takes (if 10,000mAh then double it etc.)

  • .5A (standard old styler USB charger) about 10 hours
  • 1A about 5 hours
  • 2A about 2.5 hours
  • 3A about 1.7 hours (note using a higher amperage will not damage the power bank, but it may produce more heat)

Charging Ports and Cables

Power banks usually have a single micro-USB upstream charging port.

They all have one or more downstream USB-A charging ports. The ports may be rated .5A, 1A, 2A or even 3A.

But as they are all drawing off the same battery, the Amperage rating of the devices must not exceed the rated capacity of the battery.

A tablet will draw most current. Let’s say you have a 5,000mAh power bank capable of providing 2A charging and a tablet with 4200mAh battery. It should, again, in theory, charge the device in 1 hour.

power bankAnother useful feature to consider is integrated cables. Consider power banks such as Jackery Warrior 6000  – make sure the cable connectors are compatible with the portable devices you are planning to charge.

Extra Power bank features

Here are the main extra features to consider:

  • Quick Charge – technology developed by Qualcomm that allows compatible devices to be charged up to 5 times faster compared to the standard charging times.
  • Over Voltage/Current Protection – an extra layer of protection that monitors the electric current and voltage levels generated by the portable battery charger. Keeping the current and voltage levels consistent helps to extend the battery life of the connected devices.
  • Over Charge Protection – technology that checks the battery levels of the connected device(s) and disables the charge once the battery is full.
  • Pass-through Charging – allows the power bank to charge the connected devices while charged by a USB wall charger or another power source.
  • IP rating and shockproof body – a useful enhancement for anyone doing active sport, hiking or camping as it adds water and impact protection to keep your power bank safe.
  • Solar-Powered charging – great for hikers, campers or anyone who needs to be able to recharge the power bank while in the wild. The recharge process is extremely slow, yet it allows you to stay away from a wall socket for much longer.
  • Flashlight – a built-in LED light that may be handy when travelling or camping at night.

Choosing a power bank does not need to be hard. There is a good overview of power banks here.

USB-C is different again

While this guide has mentioned specific brands, you should look at power banks from quality makers including Laser and Belkin

I am very taken with Laser’s USB-C Power Delivery 20,000mAh that delivers between 5-20V to charge USB-C devices (as well as up to four micro-USB) devices. Never travel without it!

I also like Belkin’s USB-C MIXIT with integrated cables.