How to Choose a High-Capacity Portable Charger

In selecting the best large battery bank, you have to determine whether it has sufficient practical energy to recharge your devices, will charge them quickly enough for your needs, and is within the allowable battery requirements for travel by air; the answer will be no until you confirm all of those three factors against the actual model’s specifications.

Typically, a high-capacity power bank is sold according to its milliamp hours (mAh)—that is the unit of measure used to indicate how much electrical power is stored in the battery when fully charged—and therefore you cannot compare different capacity power banks based on only the mAh value. This method of rating does not take into account the voltage that must be present to properly compare energy between batteries, does not take into consideration the fact that energy is lost in the conversion process, and provides no information concerning output to operate a laptop. Through independent discharge tests, the FAA’s passenger battery rules, the latest version of the rules governing personal battery use may be different than the current rules, and the airline policies regarding the allowable size of batteries for travel in 2026, we have a more complete picture about how to evaluate battery banks and how you can ensure those banks will meet your needs when travelling. The following are guidelines for interpreting the information that can be found on a battery bank manufacturer’s website or packaging.

Compare high-capacity portable chargers by watt-hours, not mAh

While the mAh number on any battery measures the amount of electric charge, it does not give any indication of the battery’s total capacity to store energy. Anker’s power bank label guide defines the capacity of a battery in terms of its mAh as “the total number of coulombs (MAs), or ‘coulombs’ (Ma), that the battery can hold under certain specified conditions.” Anker defines watt-hours (Wh) as the total number of watts (or power) that can be supplied by the batteries for a one-hour period. The only way to convert mAh to Wh to get energy, is to multiply mAh times volts (V). Therefore, even if two power banks have the same mAh, if they have different voltage ratings, they will have different amounts of total energy stored within each power bank, respectively.

To determine Wh, the FAA states you take the value of mAh and divide it by 1,000 and then multiply it by the number of volts in your battery. The IATA defines Wh with the same formula (Wh = Ah × V), except it uses nominal voltage. One caveat to this method is that you need to use the voltage associated with the mAh shown in the label. An example is found in Anker’s guide, which lists a usage label “Cell Capacity: 5,000mAh, 14.4VDC, 72Wh” that contains four cells connected in series. Each cell runs at 3.6 V, so the 20,000 mAh total belongs with 3.6 V:

• 20,000 mAh ÷ 1,000 × 3.6 V = 72 Wh, which matches the printed figure.
• 20,000 mAh × 14.4 V would give 288 Wh. That’s four times too high, because it mixes the summed cell charge with the series pack voltage.
• 20,000 mAh × 5 V would give 100 Wh. That’s also wrong, because 5 V is a USB output voltage, not the voltage the mAh was measured at.

Thus, for most cases, the printed Wh rating on a battery’s label is the most useful piece of information to consider and you will seldom have to calculate it. Per IATA, all lithium-ion batteries are required to have the Wh rating marked on the exterior of the portable power banks. When you create a list of the highest-capacity portable power banks, always write down the Wh of each portable power bank, treating the mAh as a third or lesser indicator of capacity.

The simplest method to understand this guide is by treating the three limitations separately. First there is an energy limitation which will be defined as the total amount of energy contained in that Bank (watt-hours). Second, there will be a limitation on the rate at which a Bank can deliver energy (in Watts), both at the port level and as a total (i.e., of multiple Ports). Third, there is a travel limitation on which Airlines permit Banks to travel. This travel limitation will typically be defined by how many watt-hours (Wh) are contained in the Bank and how many separate Bank units you take with you. Each of the three limitations can exist independently from the others; thus, a Bank could pass one limit but fail at another. Each of these limitations has its own check below.

Calculate usable energy and realistic device charges

The distinction between energy that has been stored versus that which has been delivered is where most of your users will become dissatisfied (and where confusion occurs). For example, one thread on Electrical Engineering Stack Exchange illustrates this. A user asked why they should expect to get approximately eight full charges out of their battery, which had a capacity of 10.4 Ah at 5 V, and yet the manufacturer only stated the battery would provide around 4.5 full charges. A response details how a user must calculate the energy contained within a battery using the voltage of that bank at the nominal output voltage of the cells (approximately 38.5 Wh) instead of using the 5 V output from the battery, as this is how energy is lost as well as when stepping from the 3.6V (nominal) output of the bank to the 5V USB input on the phone. The user should note, however, that it is not possible to ascertain exactly how much energy is lost when converting energy back to the phone’s internal battery since it can vary depending on temperature and discharge rates.

Independent measurements show how big the first loss can be. TechGearLab discharged each pack into a dummy resistive load through a digital multimeter, with the current set to the highest rate each pack supported. It reported that no battery pack achieved its stated capacity. Across the nine models in its comparison, measured usable capacity ranged from 68.92% to 83.57% of the claimed figure. Treat that as a range for that sample under that method, not a universal constant. Manufacturers give their own figures: Anker Canada says a power bank often provides only 70% to 90% of its label in real use. Anker’s label guide puts conversion losses at typically 10% to 15%, plus about 5% from the cable. Those are first-party claims, not independent proof.

The capacity-to-usable-energy calculator

The calculations associated with testing the battery should be performed on paper or in a note-taking application (e.g. the Notes App on an iPhone). Each calculation should show what was measured and what was estimated so that no one calculates a figure that seems to be more accurate than it really is.

1. Stored energy (Wh). Use the Wh printed on the case. If there isn’t one, calculate it as (mAh ÷ 1,000) × the nominal voltage printed beside that mAh figure.
2. Bank-side factor. If an independent lab has published a measured percentage for your exact model, use it. If not, run the calculation twice, once at 0.69 and once at 0.84. That’s the measured spread in TechGearLab’s sample, used here as an assumption range.
3. Device-side factor. This is an editorial assumption, not a measured value. Use 0.85 for a cautious estimate and 0.90 for an optimistic one, roughly in line with the 10% to 15% conversion loss Anker reports. Change it if you have better data for your device.
4. Device battery (Wh). Find this on the device maker’s spec page.
5. Estimated full charges = (stored Wh × bank factor × device factor) ÷ device battery Wh. If you don’t want to drain the bank completely, lower the result by whatever reserve you want to keep.

Using the example of Anker’s 72 Wh pack from its battery label guide, delivery of USB energy will be in the range of approximately 49.6 Wh to 60.2 Wh (72 × 0.6892 and 72 × 0.8357 on each side) or an estimated 42.2 Wh to 54.2 Wh stored in the device taking device side assumptions into account. As noted, Apple indicates that a 13-inch MacBook Air (M4) uses a 53.8-watt-hour battery, so the average is 0.8 to 1.0 full charges of a laptop; however, the 13-inch iPad Air (M4) uses a 36.59-watt-hour battery which gives an average of approximately 1.2 to 1.5 charges. If comparing the two batteries by mAh numbers would lead to a vastly different result; this is due to the fact that the voltage of a laptop’s internal battery will not be the same as the voltage of a bank’s cells which was the exact issue that caused the Stack Exchange poster’s confusion.

Checking a bank you already own

Opening the battery is not necessary to find out how much actual power it is capable of supplying. Anker Canada provides one method using a USB power meter. Charge the bank fully; plug an inline meter into the bank’s output port, then plug in either a phone or USB load tester, and keep track of the amount provided until the bank is fully discharged. The same guide points out that the quality of the cables, the fact that some phones draw an uneven amount of current depending on usage, and the ambient temperature can all make a difference on the results.

Instead of recording the mAh reading of your device, record its total watt hours (Wh). You cannot compare mAh readings taken at 5 volts to the mAh rating found on each individual cell in your battery. When performing your experiment, record the port, cable type, and temperature of the environment where the test was done so that a second experiment can be compared directly to the first experiment. Always use a commercial-grade enclosed inline-type of tester for this type of testing. DO NOT open or disassemble the testers; do NOT place any electrical shorts on their terminals when performing your tests; DO NOT connect any bare wire(s) to them.

Match USB-C output and power sharing to your devices

Capacity alone doesn’t mean that your device will receive energy at a rate that it can accept. The maximum amount of energy your device can receive depends on four factors: (1) The device’s input requirements, (2) The voltage and current profiles of the port(s) that you are using, (3) The bank’s total output when there are multiple ports in use, and (4) The type of cable you are using to connect to your device.

Let’s start with the device. Anker SOLIX recommends that laptop owners look at their power brick’s output rating and find the number of watts based on volts × amps. For instance, a 20 V × 3.25 A will equal 65 W. The same manufacturer guide also mentions that a bank that does not provide enough power may charge slowly, will charge only while the laptop is in sleep mode, or will continue to lose charge while using heavy workloads. Apple provides a 30W or 35W adapter with the 13-inch MacBook Air (M4) and says it can be charged quickly with a 70W adapter, so there is not one specific number associated with how much watts a bank can deliver to that laptop.

Next, check the bank’s port profile, rather than the largest headline wattage that it claims to have. Anker labels how much power is delivered per port on their label (i.e., USB-C 5V3A up to 20V5A), as opposed to how many Watts total banks have per port, which is noted as “Total Output: 200W Max” on their labels. Anker provides an example that describes the Laptop Power Bank can provide 165 watts to two devices at once and up to 100 watts when charging a single USB-C device. WIRED’s October 2026 roundup showed the Anker bank’s speed dropped when charging multiple devices at the same time.

Not all devices with large battery capacities will produce high levels of output; take, for example, the 20,000 mAh Mophie Powerstation XXL in TechGearLab’s spec table, which lists the product’s USB-C profiles (5 V/3 A, 9 V/2 A, 12 V/1.5 A) with a maximum output of approximately 18 W when multiplied together. A laptop requires more than this moderate level of output, even though it has a lot of stored energy available.

The cable you use to connect the power bank to your device is the final link in the charging chain. According to ChargerLab, all USB-C cables must carry at least 3 A, equating to 60 W at a voltage level of 20 V. In contrast, charging at 100 W (20 V/5 A) requires a USB-C cable with 5 A of capability and needs to have an e-marker chip installed to provide all of the necessary information to the device about the power bank’s output capabilities. The physical shape of the USB-C plug alone will not tell you anything about what the cable supports. The USB-IF Conformance Program is based upon USB Power Delivery Specification Revision 3.2, and separates its Type-C functional testing from its Power Delivery compliance testing for battery charging products. The page also notes that EU regulations allow for proprietary charging protocols; therefore, a manufacturer’s “fast charge” label or claims of standards-compliance via USB PD may be different and should be evaluated independently.

Budget for recharge time, weight, and size

The wall outlet must be used to “refill” each extra watt-hour you have on a portable power bank (PPB). The time it takes to “refill” (recharge) the PPB greatly depends on the type of charger and cable used to charge the bank, so make sure you check the test conditions to see how they compare. The TechGearLab test results for “refilling” (recharging) a fully drained Mophie Powerstation XXL were recorded as 350 minutes for the Mophie Powerstation XXL and 310 minutes for [the INIU 22.5W 20000 using a standard 2.1-amp (A) USB power brick](https://www.techgearlab.com/topics/electronics/best-power-bank/how-we-test) and either the included cable or built-in plug. A USB power brick (or charger) rated at 2.1 A at a 5 Volt (V) supply rating can deliver a maximum of approximately 10.5 watts; therefore, the times indicate the speed of the wall charger (i.e. 2.1amp USB brick), not the fastest way that each bank can be “recharged”.

It is possible to achieve a faster charge or refill if the wall charger used to recharge the bank matches the specifications of the bank (i.e., 24,000mAh Sharge 170; complete recharge in an hour up to 140Ws based on the correct cables and charger) and, in reference to the Anker Laptop Portable Battery Pack 25000mAh; it takes 2 hours to recharge (again, based on the correct cables and charger). These figures were generated using different setups from TechGearLab, so, again, you cannot compare the two directly. The most important thing you can do is look at the bank’s input specifications. The Anker example I provided states it requires input from a wall charger (or AC adapter) up to 20V5A with a 100W base input and has a maximum input of 100W. Therefore, you will need to purchase a wall charger and cables capable of providing this much power, or plan to wait until overnight for the bank to recharge slowly.

There is a significant difference in the weights of various batteries, even when both claims are being made about the same battery’s capacity. For instance, TechGearLab weighed two different batteries, with both of them being 20,000 mAh, and found one weighed 15.5 oz (439 g) for the Mophie and 12.3 oz (349 g) for the INIU. The dimensions of these two batteries were 3.12 x 6.10 x 0.97 inches (79 x 155 x 25 mm), and 2.76 x 5.27 x 1.08 inches (70 x 134 x 27 mm) respectively. The same test of the INIU 10000 revealed it weighed 6.9 ounces (196 grams). The gap in weight between the two packs mentioned above, which have the same rating, highlights how insufficient the weight of a battery is for determining if it is a fake or genuine mAh rating. If you find a battery that is significantly lighter than its claimed capacity, take a closer look. However, the casing, electronics, and cells all differ from one another, so the only way to be certain of a battery’s true capacity is to compare the documentation and perform a discharge test.

Check airline power-bank limits before you buy

Even though the bank passed all prior checks, Air Travel may disqualify you from using that bank. The FAA has stated that all lithium ion batteries (also known as lithium polymer or lithium ion polymer), including power banks, must be carried on as luggage, and may not be checked in. However, there is no consensus on the maximum watt-hour capacity that can be brought onto aircraft by an individual passenger. This is currently a point of contention within the airline industry.

On March 27th, 2026, ICAO released a notice that the number of lithium-ion battery (power bank) units that a person can take on board an aircraft will be limited to two per passenger, and that no recharging will be allowed during the flight. In addition to ICAO’s notice, IATA added another detail to its operator guidance, which states that even though ICAO lists the option of obtaining an approval for power banks with 100-160 Wh capacity in the future, IATA will not include an option for a battery of this capacity in the 68th edition of the Dangerous Goods Regulations to take effect on 1/1/27, making it a risky purchase for travelers who are going to fly via an airline. However, at present the FAA still lists an option for obtaining an approval for lithium-ion capacity batteries over 100 Wh.

In order to give clarity to the above-mentioned watt-hour capacity figure in relation to the mAh capacity figures, the following examples may be used for calculations to determine if one has purchased a lithium-ion battery: A battery with a maximum output of 100 Wh would equate to approximately 27,000 mAh at a voltage of 3.7 V, or 27,700 mAh at 3.6 V. A battery with 30,000 mAh at 3.6 V would equate to approximately 108 Wh, which will place the battery in the “disputed” range for allowable watt-hour capacity. In addition, when purchasing a battery, it is important to know if the Wh rating can be easily read from either the battery or from documentation associated with the battery’s purchase. IATA has stated that if an operator cannot verify the Wh rating from either the battery itself or from the battery’s associated documentation, the operator may prohibit the carrying of the battery on an aircraft. Additionally, many air carrier policies and/or procedures have changed regularly during the past 7 months regarding the carrying of lithium-ion batteries as checked luggage, therefore, prior to travelling on an airline, always check your specific air carrier’s policies regarding the carrying of lithium-ion batteries.

Verify the exact model, safety documents, and recall status

You cannot rely on just a name or logo to determine anything about the particular product. Work through these checks in order, and stop if a document doesn’t name the same model:

1. Read the case label. Anker’s guide says the model and ratings are usually printed on the back, side, or bottom. Write down the model number, Wh, input, per-port output, and total output.
2. Match the manufacturer’s exact-model page. Model number, revision, and Wh should be the same on the case, the maker’s spec page, and the listing.
3. Ask for safety-certification evidence that names the model. UL Solutions describes UL 2056, the Standard for Power Banks, as covering overcharge and discharge protection, short-circuit and overload, drop and impact, and thermal safety. It says it is currently the only Nationally Recognized Testing Laboratory (NRTL) that applies UL 2056. A logo in product photos isn’t the same as a certificate that identifies the model.
4. Ask for the UN 38.3 test summary. PHMSA says lithium batteries must undergo the design tests in UN 38.3, and manufacturers and distributors must make a test summary available. The summary should identify the model, Wh rating, testing lab, report details, and results. Keep in mind what it covers. IATA’s operator guidance describes UN 38.3 as a transport standard and says plainly that it “is not a consumer product safety standard.”
5. Search for recalls by model number. Anker’s history shows why the brand name isn’t enough. Its PowerCore 10000 recall applies only to model A1263 manufactured between 01/01/2016 and 10/30/2019 and sold in the US, and it was issued jointly with the CPSC. A separate program covers models A1642, A1647, and A1652. Anker tells owners of those models to stop using them, submit proof of purchase, a model-number photo, and the serial number for a replacement, and not to return them to Amazon or throw them in household trash or store recycling bins. Follow the remedy in the notice for your exact model, and search the CPSC recall database for anything else you’re considering. The FAA also says recalled batteries must not be carried aboard unless they’ve been removed or made safe.
6. Confirm who’s selling it and who honors the warranty. On a marketplace, the seller may not be the manufacturer. Find out who handles returns and warranty claims, and whether that seller can produce the documents in steps 3 and 4. The same seller-and-document checks apply to wall chargers, which a companion guide on marketplace charger checks covers.

Regardless of what store you purchase from, the Amazon portable power bank with all six steps documented will be a lot more informative than the big box store listing that skips all six steps. A product with no documentation of the six stages and all other required documentation for a complete review should be removed from your list of prospective purchases, even if its capacity claim looks great.

Choose the capacity class that fits the job

After going through the three limits and document checks, how to choose your high-capacity portable charger will come down to determining your capacity class, as there is no one size fits all. There isn’t one best high-capacity portable charger for every buyer. The matrix below will give you a general idea of how different high-capacity chargers are configured. The delivered energy column takes TechGearLab’s measured range of 69% to 84% of typical Wh stored and should be used as an estimate of delivered energy, not as a measurement of a specific bank.

The mid-row configuration is the best option for most buyers flying with their laptops. It offers laptop output capability and falls within the 100 Wh limit, but is heavier than a phone-first bank and requires more to recharge quickly. If you only need to charge phones, the top-row configuration is better suited, as it weighs less and is more convenient to carry around. The lower-row configuration is best for road trips or backup use at home, where air travel restrictions don’t apply. Regardless of which configuration you choose, you should still refer to the document checks listed above to determine if the specific listing you are considering is worth purchasing.

The Capacity That Matters

When deciding how much power a power bank can actually give you, make sure to consider the following three things: The Energy (Wh) of the Battery (often expressed in watt-hours) of your Device, How many watts your device’s charger is rated for (this varies greatly between devices), and which airline will have the strictest policy regarding battery watt-hours. Before I begin shopping, I will calculate my Battery’s Watt-Hours, my charger’s Watts, and the strictest Policy that an Airline will have for batteries. I will do this for every Bank I consider. I can immediately disregard Banks (models) if their specifications do not add up. I will also choose the smallest Bank that meets all three criteria. The extra weight and time spent charging should result in usable energy.

Frequently Asked Questions

Can I fly with a 30,000mAh power bank?

A 30,000mAh Battery at 3.6V nominal voltage is approximately 108Wh. U.S. FAA guidelines state that you’ll need the permission of the airline to transport this battery within that Wh range, and according to IATA’s Table of 2026, there are no allowed power banks for any capacity higher than this. Be sure to check the printed Wh on your battery pack and verify your airline’s operating policy regarding carrying power banks.

What if the Wh marking on my bank has worn off?

According to IATA guidelines, airline staff may ask for proof of the battery’s Wh rating from either the battery or the documentation supplied with it, and if neither document confirms the battery’s Wh rating, the airline may refuse to carry it. Therefore, be sure to bring along a copy of your power bank’s usage instructions or an electronic printout of the manufacturer’s specifications.

Can a power bank charge my phone while it recharges itself?

If your power bank is capable of “pass-through” charging, it can be charged from an outlet while simultaneously charging the connected device. Only certain models can do this; WIRED mentions that Anker has created a Laptop Power Bank that allows pass-through charging. To confirm if your model supports pass-through charging, please consult the manufacturer’s instructions.

Is a high capacity portable battery from Amazon riskier than one from a store?

When purchasing a power bank, the retailer you buy from is not as important as ensuring that you have the correct supporting documents that prove that the power bank meets all relevant safety requirements. All retailers will check all of the same types of documentation: the battery must match the manufacturer’s model number, provide a safety certificate for that model, have a summary of the UN 38.3 testing results, be included in a recall database, and have clear contact information for the seller and warranty.