Power banks come to the rescue far from electrical 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 to a conventional laptop.

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

1. How long will a power bank with a capacity of 10,000 mAh last?

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

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

In terms of the ratio of capacity to the size of the power bank case, the winner is the 10,000 mAh model, which is most popular among colleagues in the portable battery industry. A full charge of such batteries is enough for about one and a half to two complete procedures for “refueling” a battery with a capacity of about 4000 mAh. It will not be possible to squeeze all 10,000 mAh out of the power bank due to the difference in voltage between 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” is lost. But this is the topic of the second question.

Powerbank batteries 7,001 – 10,000 mAh

2. Why is the actual capacity of the power bank less than the “passport” capacity?

The actual capacity of a 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 by the operating voltage of its own battery (3.6 or 3.7 V), then dividing by the 5 volt 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 model BASEUS Bipow 18W 10000 :

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 declared capacity by a factor of 1.6, which already takes into account the waste 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 :

20000 mAh / 1.6 = 12500 mAh.

3. What is fast charging in a power bank?

The ability of the power bank to operate in fast charging mode significantly reduces the time it takes to refuel compatible gadgets. However, to use this function correctly, it is necessary that both the external battery and the device being charged support the same accelerated charging format. This technology, broken down by each type, is described in detail in the material “Fast charging for smartphones: types and generations.” All types of accelerated charging described in the article are used on board power banks. External batteries often provide maximum charging power when connecting one consumer - in multiport models, when distributed to several devices, the power strength for each of them is reduced or even divided proportionally.

Power banks with fast charging significantly reduce the time it takes to recharge compatible gadgets.

A separate point of the program in the characteristics of portable batteries is fast charging “in its own 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 an additional battery is always ready.

External batteries with fast charging

4. Which power bank is suitable for a laptop?

A laptop is a rather voracious device in terms of energy consumption. Accordingly, not all power banks are suitable for recharging it. External batteries with support for Power Delivery technology, capable of transmitting high power and power (up to 100 W) through the USB C connector, cope well with the tasks of powering laptops. For the portable charger to work correctly, you will need a suitable 3.1 cable.

But what about laptops whose interface shelf does not have USB C connectors with charging support? Power banks have another answer to this - individual models, specially designed to maintain the viability of portable computers, can be equipped with a variety of adapters for organizing power supply for almost any device. These copies are initially designed for high output voltages and currents.

Powerbank batteries with Power Delivery

5. Is it possible to use a power bank as an uninterruptible power supply?

In case of a power outage, power banks will help to establish autonomous operation of some volatile devices in the manner of Wi-Fi video surveillance cameras powered via the 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, while devices of the second order will provide users with a stable connection to the Internet.

External batteries with Power Delivery support are often used to ensure laptops are energy independent from a power outlet.

As an uninterruptible power supply, the corresponding models of external batteries will also support the connection of the above-mentioned laptops, portable audio speakers and other devices with suitable voltage and power parameters. But don’t expect to power a power-hungry kettle or washing machine from a power bank - if there are frequent power outages in country households, it’s better to look for a backup generator.

6. What happens if you connect a power bank to yourself?

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

Let’s complicate the task: what if you connect one external battery to another? Will we get a perpetual motion machine and will devices be able to charge each other endlessly? Also no. Since there are losses when releasing a charge (remember the debriefing on the second question), power banks will be able to charge each other only to a certain percentage corresponding to the efficiency value (85-90%). In cyclic operation they will gradually discharge. However, 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 directly to the output connector of the device, power banks usually get along with a solid “A”.

7. Is it possible to take a power bank on a plane?

Since April 1, 2016, the International Civil Aviation Organization has banned the carriage of lithium-ion batteries in the luggage compartment of aircraft. The risk of spontaneous combustion of batteries is a concern. And although in truth the ban applies 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 carried primarily in hand luggage.

A prerequisite for bringing 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 an external battery should not exceed 100 Wh for transportation without approval and no more than 160 Wh, subject to prior receipt of permission to transport the power bank from a representative of the air carrier. In any case, it is better to check these points with the specific airline in advance.

8. How does a wireless power bank work?

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

The over-the-air charging process usually starts automatically when detected on the device's induction panel. In some cases, it must be activated with a button on the body of the portable battery. Note that the wireless charging power of the vast majority of power banks is usually low and amounts to 10 W.

Powerbank with wireless charging

9. How to turn off the power bank?

As a rule, the portable battery turns off automatically when the charging cable is disconnected or when there is no power-consuming device at the wireless charging station. However, a number of models provide a charging mode for low-power devices, which they do not enter and do not automatically exit. Such a charging program is activated by pressing the function button and it is launched differently in different versions of power banks.

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

Using the example of the popular external battery Xiaomi Mi Power Bank 2S 10000, the low power charging mode is activated by double pressing the function button. In it, the connected gadget is charged for two hours, after which the mode turns off. If you need to exit a low-power program early, just press the same button once.

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

To recharge Apple equipment, power banks that support the Power Delivery protocol are suitable. Together with them it is supposed to use a corresponding wire with a Lighthing connector at the “tip of the tail”. It is advisable to give preference to certified external batteries with the MFI mark, 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 testing in this regard.

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

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We suggest reading other articles on portable external batteries in the section “All about powerbank batteries”.