Power banks come to the rescue far from electric civilization, when there is no way to quickly use the usual outlet to recharge a smartphone or dead headphones. And some of the external batteries are strong enough to provide power supply to a conditional laptop.

Most often, users ask the following question regarding portable batteries:

1. How long will a 10000 mAh power bank last?

Capacity is the determining parameter when choosing a power bank. The higher it is, the more times it will be possible to refuel a smartphone, tablet or other devices from the category of portable electronics without the need to replenish energy reserves in the cells of an external battery.

Models with a battery capacity of 10,000 mAh are the main backbone of power banks.

In the ratio of capacity to the size of the body of the power bank, 10,000 mAh models win, which are most widely used among colleagues in the portable battery shop. A full charge of such batteries is enough for about one and a half to two complete “refueling” procedures for a battery with a capacity of about 4000 mAh. It will not work to squeeze out all 10,000 mAh from the power bank due to the difference in voltage on the batteries of the external battery (3.6 or 3.7 V) and the standard USB bus voltage (5 V), during which the treasured “mAh” are lost. But this is the subject of the second question.

Power bank batteries 7001 – 10000 mAh

2. Why is the real capacity of the power bank less than the "passport"?

The real capacity of the power bank is always lower than the nominal capacity due to the aforementioned need for voltage conversion, which is accompanied by “mAh” losses. The actual capacity of an external battery can be determined by multiplying it by the operating voltage of its own battery (3.6 or 3.7 V), then dividing by 5 volts of the USB interface and multiplying the result by the efficiency (in modern models it is about 85%, i.e. 0.85).

Take, for example, the popular BASEUS Bipow 18W 10000 model:

10000 mAh ∙ 3.7 V / 5 V ∙ 0.85 = 6290 mAh.

Sounds too complicated? There is a second option: the approximate real capacity of the power bank is calculated by dividing the claimed capacity by a factor of 1.6, which already takes into account the expenditure of part of the energy on third-party functions and losses during its transmission.

We will perform the calculations using the example of the Xiaomi Redmi Power Bank 20000 power bank :

20000 mAh / 1.6 = 12500 mAh.

3. What is fast charging in a power bank?

The ability of the power bank to work in fast charging mode significantly reduces the time to refuel compatible gadgets. However, for the correct use of this function, it is necessary that both the external battery and the device being charged support the same format of accelerated "refueling". Details about this technology, broken down by each type, are described in the material Fast Charging for Smartphones: Varieties and Generations. All types of accelerated charging described in the article are used on board power banks. External batteries often give out maximum charging power when one consumer is connected - in multiport models, when distributed to several devices, the current strength for each of them decreases or is even divided proportionally.

Power banks with fast charging significantly reduce the time of refueling compatible gadgets.

A separate item in the programme in the characteristics of portable batteries is fast charging “in your direction” - the ability to charge from adapters that support the appropriate fast charging technology. In such models, the capacity of the built-in battery is replenished faster and thus the additional battery is always ready.

Fast Charge External Batteries

4. Which power bank is suitable for a laptop?

A laptop is a rather gluttonous device in terms of power consumption. Accordingly, not all power banks are suitable to ensure its recharging. External batteries with support for Power Delivery technology, capable of transmitting high power and strength current (up to 100 W) through the USB-C connector, do a good job of supplying laptops with energy. For the portable "charger" to work correctly, you will need a suitable 3.1 standard cable.

But what about laptops that do not have USB-C connectors with charging support in the interface shelf? Power banks have another answer to this - individual models for maintaining the viability of portable computers can be equipped with a variety of adapters for powering almost any device. These instances are initially designed for high output voltages and currents.

Power bank batteries with Power Delivery

5. Can I use a power bank as an uninterruptible power supply?

In the event of a power outage, power banks will help to establish autonomous operation of some volatile devices in the manner of Wi-Fi surveillance cameras powered by USB 5V bus, or LTE modems. Devices of the first order will be able to continue to keep abreast of events happening at home or in the office, the second - will provide users with a stable connection to the Internet.

External batteries with Power Delivery support are often used to ensure the energy independence of laptops from an outlet.

As an uninterruptible power supply, the corresponding models of external batteries will also pull the connection of the aforementioned laptops, portable audio speakers and other devices with suitable voltage and current parameters. But don’t count on powering a voracious kettle or a washing machine from a power bank - if there are frequent power outages in suburban households, it’s better to look after yourself a backup generator.

6. What will happen if you connect the bank to yourself?

Oddly enough, no violations of the space-time continuum will happen - the protection system will work at the bank and nothing will happen. Modern portable batteries have integrated protection systems against excessive voltage, overheating, short circuits and overloads to avoid damage to the gadget.

We complicate the task: what if we connect one external battery to another? Will a perpetual motion machine turn out and will devices be able to endlessly charge each other? Also no. Since there are losses when releasing a charge (remember the debriefing on the second question), power banks will only be able to charge each other by a certain percentage corresponding to the efficiency value (by 85-90%). In cyclic operation, they will gradually discharge. At the same time, it is not a fact that the controller will effectively cope with charging and discharging energy at the same time.

But with pass-through charging, when the portable battery is connected to an external power source, and the gadget being charged is connected directly to the output connector of the device, power banks usually get along with a solid “five”.

7. Can I take a power bank on a plane?

Since April 1, 2016, the International Civil Aviation Organization has banned the transportation of lithium-ion batteries in the luggage compartment of airliners. Concerns are raised by the risk of spontaneous ignition of batteries. And although in truth the ban refers more to the transportation of external batteries on an industrial scale, some airlines took it literally - according to their rules , power banks can only be taken in hand luggage.

On airplanes, power banks can be transported mainly in hand luggage.

A prerequisite for carrying a portable battery on board is the presence of identification markings on the case indicating the capacity of the power bank. “Chargers” up to 20,000 mAh are allowed for transportation in hand luggage. According to other requirements, the energy intensity of the external battery should not exceed 100 Wh for transportation without approval and not more than 160 Wh, subject to prior receipt of permission to transport the power bank from the representative of the air carrier. Anyway, it is better to check these points with a particular airline in advance.

8. How does wireless power bank work?

The wireless charging method eliminates the fuss with wires and reduces the wear of connectors both on the devices being charged and directly on the power bank with the support of the appropriate technology. The induction work surface on the back of such devices provides “refueling” of compatible gadgets literally “by air”. External batteries work with wireless charging according to the Qi standard, which is supported by many smartphones, headphones and smartwatches.

The “over-the-air” charging process usually turns on automatically when it detects a device on the induction panel. In some cases, it must be activated with a button on the body of the portable battery. Note that the power of wireless charging in the vast majority of power banks is usually small and amounts to 10 watts.

Wireless Power bank

9. How to turn off the power bank?

Usually, the portable battery turns off automatically when the charging cable is disconnected or when there is no power consuming device on the wireless charging station. However, some models provide a charging mode for low-current devices, in which they do not enter and do not automatically exit. A similar charging programme is activated by pressing the function button and it starts differently in different instances of power banks.

To work in low-current charging mode, some power banks must be turned on and off.

Using the popular Xiaomi Mi Power Bank 2S 10000 external battery as an example, the low current charging mode is activated by double-clicking the function button. In it, the connected gadget is charged for two hours, after which the mode is turned off. If necessary, exit the low-current programme ahead of time, just press the same button once.

10. Which power bank is suitable for iPhone or iPad?

For recharging "apple" technology, power banks with support for the Power Delivery protocol will fit. Together with them, it is supposed to use the appropriate wire with a Lighthing connector at the “tip of the tail”. It is desirable to give preference to certified external batteries with the MFI brand, which stands for "Made for iPhone/iPad/iPod". The presence of a certificate means that the power bank was created with the expectation of full compatibility with Apple portable electronics and has successfully passed the test on this occasion.

Specially for the latest generations of iPhone, external batteries with a magnetic Mag Safe mount are produced, allowing you to “glue” the charger to the phone from the back. The portfolio of the Cupertino brand even has a branded mini power bank Apple MagSafe Battery Pack.

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For other articles on portable external batteries, we suggest that you read the section "All about power bank batteries".