How does a power bank work?

Technology and our handheld devices have seemingly become an extension of ourselves, your arm never feeling complete without a phone or smartwatch tethered to the end. We already feel anxiety pulsating through us just thinking about a “Battery at 10%” message popping on the screen.  But how does a power bank work?

But power banks have seemingly eradicated the need for concern. Handy little devices that can now prolong our dependence with a few hours by giving our devices some juice.

Power banks are becoming smaller, stronger, and more portable than ever before and soon before long the “my battery ran out” excuse will just not suffice. 

But what exactly are these little “life-giving” boxes and what sorcery is happening internally?

How does a power bank work?

A very short answer to this question is – it is a portable battery. An outwardly simple gadget that uses some pretty complicated technology. The internal circuitry is wired in such a way that you never overcharge a device and there are plenty of internal power conversions happening, unseen by the naked eye.  

Inside the outer casing is a battery, these are what will store your power (like a bank). The device must first be charged by plugging it into a power source and allowing it to charge up the internal battery. At this time, the power flow is input to the power bank device. In layman’s terms, you give it some power to later get some power.

Once the device is charged, it will retain the electrical charge for up to a few months. When you want to charge your laptop, phone, or other electronics, you simply insert a USB power cable into the power bank and your device, the cable will transfer the charge out from the power bank, and transfer it across to your device. 

Types of batteries

Power banks tend to use two types of batteries; Lithium polymer or Lithium-ion. So which one is best for your needs?

  • Lithium polymer batteries are incredibly safe to use, often using flexible packaging with aluminum, which protects from any kind of explosion or hazardous situation. They are lightweight, which is a large part of the reason they are more expensive. They are less dense, which reflects that they have a shorter life span and essentially offer fewer recharges over time. They are used more in new technologies because they can be molded into different shapes to fit inside electronic devices. These batteries are usually flat and rectangular.
  • Lithium-ion batteries are cheaper to produce, and consequently also cheaper for consumers to purchase. They can potentially store 3 to 4 times more charge compared to other batteries of similar size. They also last longer over a period of time and can be recharged more times. There can however be problems storing the batteries, they do not like high temperatures; which could be a consideration if you are buying a device to take with you on your next trip to Mount Vesuvius. Lithium-ion batteries are cylindrical and resemble batteries in your TV remote. There can be one or multiple of these used in a power bank.

Both these batteries have internal capacity, measured in mAh, and nominal voltage measured in V.

How long will a power bank last?

Figuring out how many charges a power bank will give you is not as simple as you might think. First, you need to understand all the various indications. 

What is mAh?

This tells you the number of hours the power bank can sustain the current. Normal smartphone adapters have a 1000mA output. Thus, an hour of charging will fill your phone with 1000mA of power. But you are mistaken to think that a 5,000 mAh power bank can charge your phone 5 times. 

The indication of mAh is merely the internal capacity of the battery. It is not what the power bank is able to deliver on output. 

What is volt?

The voltage of a power bank, or the nominal power, indicates the battery strength. Most power banks are 3.7 volts but the output voltage can be higher. All power banks have an output of 5V or higher.

It is important to note that when more than 1 Lithium-ion battery is used, the voltage does not increase. The mAh capacity increases as the batteries are connected in parallel and the capacity is added together. The voltage however stays consistent and does not accumulate. 

Calculating the actual capacity of a power bank

It is time to do some math.

Firstly, the nominal voltage (for example 3.7V) needs to be converted to the output voltage of usually 5V. 

Next, one must also factor in that the power bank will not deliver 100% of its charge available. The circuit will use energy too and over time the capacity depletes. The quality of components in the circuit will determine the rate of energy loss, i.e. more expensive parts, less energy lost. 

Thus, it is understood that one should determine the energy efficiency of a power bank instead of the actual output strength or capacity. The efficiency can be expressed as a percentage and is a ratio of the stored energy and the supplied energy.

These formulas could help you determine these numbers if you want to get very technical:

Stored Energy (Wh) = [Internal Capacity (mAh) x Voltage (V)] / 1000

Energy Efficiency (%) = [Output Energy (Wh) / Stored Energy (Wh)] x 100

Usable Energy (Wh) = Stored Energy (Wh) x (% /100)

Actual Output Capacity (mAh) = [Output Energy (Wh) / Charging Voltage (V)] x 1000

Sizes of power banks

  • Small power banks (up to 7,500mAh) – usually enough to charge a smartphone once.

Lightweight, small in size, and very portable – a small power bank is perfect to keep in your bag for everyday use. They could be kept in a handbag or backpack for emergency use. The low cost means that they will probably give your electronic device a quick top-up, to make sure you can take notes or send an important text. 

You know those cheap branded chargers you got at the company golf day? It’s more than likely one of these and would need charging on a daily basis.

  • Medium power banks (7,500-14,999mAh) – usually enough to charge a smartphone 2 times.

This type of power bank would suit medium usage, so possibly the right type to buy if you travel for business or use your phone a lot over the course of an average day. You wouldn’t necessarily need to recharge it every day, maybe just a few times a week.

  • Large power banks (more than 15,000mAh) – usually enough to charge a smartphone 4 or more times.

For people who regularly use a lot of electrical equipment every single day (digital nomads, web designers).

Or, if you are going to live overseas for a long time like a digital nomad and might travel to some remote areas where consistent power supply can be an issue. They will inevitably weigh more in your bags, so make sure you factor it in when you have to take a suitcase onto an airplane.

By now we should have a good idea of how a power bank works, but which power bank do you need?

Best power banks on the market

Best value for money power bank

Inu Portable Charger

Power: 10,000 mAh

A slim-line, sleek-looking power bank, with a cool luminous paw print design. The size is especially impressive in light of the fact that it offers three total ports. All three delivers roughly the same charging speeds, so you can trust that your devices will share the power equally. Good for those who don’t want to splash the cash.

Best powerful power bank

ROMOSS 60000mAh Power Bank

Power: 60,000 mAh

Ultra-high capacity, this choice provides more than 12 full charges for iPhone 11 and almost 21 full charges for iPhone 8 which is extraordinary!

Charging multiple devices is no problem for this beast of a power bank. Multiple types of power cables can be used, so this has got you covered for those with high-performance charging requirements.

Best power bank for traveling

Anker PowerCore Slim 10,000

Power: 10,000 mAh

Despite being light in weight (208 grams), Anker has designed it to be durable and road-ready, with a scratch-proof, durable case. It has both Micro USB and USB-C ports for charging your devices. It is about the same size as a passport, so perfect to slip in a pocket when you are about to hit the road.

Best power bank for larger devices

Renogy power bank for larger devices

Renogy 72000mAh Laptop Power Bank with 12V Socket

This portable charger can pump plenty of power to multiple devices simultaneously. The combination of its high capacity and cigarette lighter port even make it suitable for charging more powerful devices than just laptops. It features a charging pad, which makes topping up your phone wirelessly super easy.

Best solar charger

Yelomin Solar Charger Power Bank

Portable solar charger, featuring a compass and two super bright LED lights making it perfect for any outdoor adventurer. The primary way to charge it is via USB, but the solar option (2W monocrystalline plate), and the fact it is waterproof, means you will be covered for any eventuality that could happen on a hiking or camping trip.