Published on 29th July, 2014 by Cable Chick

What Are Power Banks and How Do They Work?

What Are Power Banks and How Do They Work?

Power Banks are all the rage, but what are they for? We explore their potential, and how to choose the right one.

What is a Power Bank and what can they charge?

How Power Banks Work DiagramPortable Power Banks are comprised of a special battery in a special case with a special circuit to control power flow. They allow you to store electrical energy (deposit it in the bank) and then later use it to charge up a mobile device (withdraw it from the bank). Power Banks have become increasingly popular as the battery life of our beloved phones, tablets and portable media players is outstripped by the amount of time we spend using them each day. By keeping a battery backup close by, you can top-up your device(s) while far from a wall outlet.

The Power Banks we're talking about are good for almost any USB-charged devices. Cameras, GoPros, Portable speakers, GPS systems, MP3 players, smartphones and even some tablets can be charged from a Power Bank - practically anything that charges from USB at home can be charged from a Power Bank - you just have to remember to keep your Power Bank charged, too!

Power Banks may also be known as Power Stations or Battery Banks, too.

What types of Power Banks are there?

Cable Chick specialises in two of the three major types of Power Bank found on the market today:

  1. Our speciality is the Universal Power Bank. They come in many sizes and configurations which can be tailored to your device requirements and to your budget.
  2. We also carry a Solar-Charged Power Bank. They have photovoltaic panels which can trickle-charge the internal battery when placed in sunlight. Solar charging isn't fast, so they can usually charge via cable as well.
  3. The third type of Power Bank is the older-style battery phone case. While they can be handy, this type of Power Bank has very narrow device compatibility, so Cable Chick does not stock them.

How do I charge a Power Bank?

Power Bank Charging DiagramMost commonly, a Power Bank will have a dedicated input socket for receiving power. This power can come from a USB socket on your computer, but may charge faster when using a wall socket adapter. We most often see Power Banks use a Mini or Micro-USB socket for charging, and full-sized USB sockets for discharging. On very rare occasions, Power Banks can use the same socket for input and output, but this is rare and should not be assumed of any Power Bank, as trying to force power into an output can damage the battery. Always check the manual for specific instructions if you're not able to find a clearly marked input socket.

Depending on the capacity of the Power Bank and its current charge level, it can take quite a while to fill up. For example, a 1500mAh rated Power Bank should take about the same time as your typical smartphone to charge. For larger banks, this time can be doubled, tripled or quadrupled. Most Power Banks have both an LED indicator to show when they are at capacity, and a safety cut-off to prevent overcharging and overheating. Whenever possible, remove the Power Bank from charge when it is full, or at least avoid leaving it connected long-term after its full. Ambient temperature and power flow will also affect charge times, so it's best to keep it topped off regularly.

Some Power Banks don't work well with high-capacity chargers (like the ones that come with iPads). Trying to fast-charge a Power Bank from a 2A charger can result in damage to the internal circuitry, which isn't covered by warranty.


How long does a Power Bank last?

This is a bit of a loaded question. There are two important life expectancies to consider:

  1. The number of charge/discharge cycles a Power Bank can reliably perform in its lifetime.
  2. How long a Power Bank can retain its charge when not in use.

The answer to point one can differ between models of Power Bank, their internal components and the quality of their manufacturing. We try not to stock Power Banks which have fewer than 500 charge cycles in them. This would allow you to charge a device from the Power Bank every day for a 1.5 years before it started to lose its ability to hold charge long-term. Better and more expensive Power Banks can last longer, while smaller and cheaper units may fall short depending on their treatment. Power Banks are generally not used daily, so they often last much longer than 18 months in real-world usage patterns.

Point two depends on the quality of the controller circuitry and battery cells. A good Power Bank can hold charge for 3 to 6 months with minimal loss. Lower quality Power Banks may struggle to retain a useful charge more than 4 to 6 weeks. In this regard, you get what you pay for, and if you need a long-term emergency power supply consider increasing your budget to ensure you're not going to be caught short. Most Power Banks will slowly lose charge over time, to a degree influenced by the environment and their treatment. For example, leaving a Power Bank in the car where the temperature can fluctuate greatly over time can shorten its lifespan.

How many times can a Power Bank charge my device?

At Cable Chick, we use an icon system to indicate how many device charges you're likely to get out of a Power Bank before it needs to be recharged. Our figures are based on a formula which assumes an average device capacity of 1500mAh, a device power level of no less than 20%, and an 80% Power Bank efficiency rating. Many Power Banks boast efficiency ratings up to and over 90%, but we find that real-world usage in Australian climates typically ends up with an 80% efficiency rate. We also like to err on the side of caution to give you a conservative estimate rather than make outrageous claims. Generally, the bigger the Power Bank and the smaller the device you're charging, the more goes you get. Other factors can also improve or limit the discharge potential of a Power Bank, so look after them and they'll work better for longer.

Our Formula:
Power Bank Rating (mAh) × Efficiency × Device Depletion ÷ Device Capacity (mAh)

6000 × 0.8 × 0.8 ÷ 1500 = 2.5 charges (approximately)
6000 mAh Charge Capacity Guide

Look for our handy icons to immediately see the charging potential of our Power Banks for use with smartphones, or use this formula yourself to calculate the number of charges any device could get. All you need to know is the mAh rating of its battery!

Technical Term Glossary

What does mAh mean?
Batteries common to mobile devices and Power Banks are rated on their ampere-hours, measured in milliamps to create non-decimal numbers. The mAh ratings denote capacity for power flow over time.

Li-Ion & Li-Polymer
Lithium-Ion and Lithium-Polymer batteries are the most common rechargeable cell types found in Power Banks. Lithium-Ion cells are generally cheaper and limited in mAh capacity, while Lithium-Polymer cells can be larger and don't suffer from a memory effect over time.

When power is transferred, there is always loss due to resistance. Power Banks are not able to transfer 100% of their actual capacity to a device, so we factor in this loss when calculating how many times an average device can be charged from a fully powered Power Bank of any given size. Efficiency ratings differ between Power Banks based on their cell type, component quality and environment. Ratings between 80% and 90% are the current industry standard. Beware of suspiciously low-cost options claiming efficiency ratings of over 90%.

Device Depletion
This is the state of the battery in the device you wish to charge. The lower its power, the more a Power Bank has to work to bring it back to life. We consider charging from 20% to 90% a full charge, as the efficiency loss increases beyond these points, leading to wasted charging potential. Going from 5% to 100% can take exponentially more power.

Choosing the right Power Bank

The two major factors in choosing a powerbank come down to capacity and budget. Using the formula above, you can discover what capacity will be right for your on-the-go charging needs. From there, you can go for a cheaper power bank to save some dollars, or splurge on a high-tech option which may offer things like a slimmer form factor or more charging ports.

See our range of Power Banks

Too much Power?

If you're spoiled for choice and need to know more about our Power Banks, just contact us! We'll put the power in your hands - no worries!

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