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

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.