Power Banks - Is the juice worth the squeeze?

How does a Power Bank work?

Since power banks are basically regular batteries with some extra features, they work just like any other battery that is rechargeable. They store energy up to their maximum capacity and then release it when connected to a compatible device that needs recharging. It is as simple as that. 

What type of Batteries do Power Banks use? 

Power banks generally come with either Lithium-Polymer (Li-Po) and Lithium-Ion (Li-Ion) batteries. Of the two Li-Ion power banks are more popular.

In terms of differences between these two types:

• Lithium-Polymer batteries have a higher energy density, but they tend to have a shorter lifespan and are also more expensive to manufacture. They’re also less prone to explosion.

• Lithium-Ion batteries, on the other hand, have a slightly lower energy density but they can withstand more charge/discharge cycles and are generally less expensive.

Charging a Power Bank

The most efficient way to charge a power bank is to use a wall charger that can deliver a high power output. Using a low-quality wall charger that only delivers 2A for example, can extend the recharging time for several hours. Another way to charge a power bank is by using a charging station. Other ways to charge a power bank are using your laptop USB port, a car cigarette lighter, or using a solar charger like in the case of the BigBlue 28W or the Anker 21W. However, all these methods are slower and you should avoid them unless you can’t access a wall charger.

It’s important to avoid overcharging your power bank. This can be damaging to the battery in the long run. This is why after plugging it in, you should check the charge indicators from time to time. Some power banks, however, do come with overcharging protection so you don’t need to worry about it. Check your user manual to see if your portable charger has this feature or not.

In all the scenarios, it is recommended that you follow the manufacturer instructions associated to the power banks. In some cases, they may recommend that the power bank be fully discharged from its factory condition and then be recharged. In some cases, the power bank can be recharged right from its box. The same goes with the wall adapters in case you choose to use one that did not come with the product.

Power Bank Capacity

All power banks are different even though, on the surface, many look similar. As mentioned in the point above, most power bank units will fall into one of two categories focused on lithium technology. All power banks use rechargeable batteries, but one may use lithium-ion whereas another may use lithium-polymer. The most significant difference between the two types is the chemical electrolyte between their positive and negative electrodes. This boils down to lithium-ion holding a higher power density and a lower cost compared to lithium-polymer. However, lithium-polymer batteries are more robust, flexible, and have a lower chance of suffering with leaking electrolyte. Both forms of battery work effectively and have their pros and cons. However, it will largely depend on the design and manufacturing of a power bank as to whether it delivers the charge you need.       

All power banks have a listed capacity which is the value that the manufacturer claims for the design of that battery, whereas the real capacity is a property of that battery at a given moment in time and conditions. The real/actual capacity of a battery varies from rated capacity because of manufacturing tolerances. It decreases with consumption, and also depends upon temperature and discharge rate.

How long does a Power Bank last?

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.

 Efficiency

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.

Do I Need a Power Bank?