Key takeaways
- A power bank's quoted capacity is not the energy you get out. Expect noticeably less than the headline mAh because of conversion losses.
- For flying, power banks go in hand luggage, and most airlines allow up to 100Wh without special approval. Check your airline.
- Match the charger wattage to your device and make sure the cable can carry it.
- Choose reputable brands with proper safety markings. Cheap unbranded chargers are a risk.
In this guide
Chargers and power banks look simple, but their specs are full of jargon. This guide translates the numbers so you buy the right one and stay safe when you travel.
Capacity: mAh versus Wh
Power bank capacity is quoted in mAh (milliamp-hours). It is useful for comparing banks, but it does not mean you will get that many mAh out. The bank has to convert its internal voltage to the voltage your phone charges at, and some energy is lost as heat. In real use, expect roughly two thirds of the stated figure to reach your device.
A quick example: if your phone battery is about 4,500mAh and your power bank is 10,000mAh, you will usually get a little over one full charge, not two.
Wh (watt-hours) is the more useful unit for flying, because airlines use it. You can estimate it as: mAh x 3.7 volts ÷ 1,000. A 10,000mAh bank is around 37Wh.
Flying with a power bank
Rules vary by airline and country, so always check yours, but the general pattern is:
- Power banks go in hand luggage, never in checked baggage.
- Up to 100Wh is generally allowed without special approval.
- Between 100Wh and 160Wh usually needs airline approval, and the number you can carry is limited.
- Keep terminals protected from short-circuiting and do not use damaged units.
Power: watts and USB-C PD
Charging speed is about watts. Typical needs:
- Phones: often around 20 to 30W for fast charging.
- Tablets: around 30W.
- Laptops: commonly 45 to 100W.
USB Power Delivery (PD) is the common standard for fast charging over USB-C. Your device and the charger must both support it, and the cable must be rated for the wattage too. A basic cable can limit the speed, so buy a cable rated for the power you want.
GaN chargers
Chargers built with gallium nitride (GaN) are usually smaller and run cooler at the same wattage. They are especially useful if you travel and want one charger that handles a phone, tablet and laptop.
What to check on a power bank listing
- Real capacity compared with the headline figure and any independent reviews.
- Output ports and wattage, including whether it can charge two devices at once.
- Pass-through charging, if you want to charge the bank and your phone together.
- Size and weight, which matter more than people expect for daily carry.
- Wireless charging, if you want it. Magnetic wireless standards exist, so check compatibility with your phone.
Safety
- Buy from reputable brands with proper safety marks. Counterfeit and unbranded chargers are a fire and shock risk.
- Do not use damaged cables or swollen power banks.
- Do not charge under pillows or blankets where heat can build up.
- If a power bank or charger overheats, smells or swells, stop using it.
Common mistakes
- Buying on mAh alone.
- Ignoring the cable, then wondering why charging is slow.
- Forgetting that very cheap, unbranded units cut corners on safety.
- Packing a power bank in checked luggage.
Which one should you choose?
- Daily phone top-up: a slim power bank of about 10,000mAh is easy to carry and gives roughly one full charge.
- Long trips or camping: a larger bank of 20,000mAh or more, mindful of the airline limit if you are flying.
- Laptop users: a bank that supports high-wattage USB-C PD output, and a cable rated for that power. Check your laptop's charging requirement first.
- Travellers with many devices: a compact multi-port GaN wall charger can replace several chargers in your bag.
- Wireless charging fans: choose a bank with wireless charging only if you accept slower charging and some extra bulk.
A short glossary
- mAh: milliamp-hours, a measure of battery capacity.
- Wh: watt-hours, the energy figure that airlines use.
- PD (Power Delivery): a USB-C fast-charging standard.
- GaN: a semiconductor material that lets chargers be smaller and cooler.
- Pass-through: charging the power bank and a device at the same time.
- E-marked cable: a USB-C cable with a chip that tells the charger it can carry higher power.
Browse the current listings in our Electronics & Audio department, and read our guide to choosing noise-cancelling headphones if you are building a travel kit.
Frequently asked questions
How many times can a power bank charge my phone?
Divide the power bank's capacity by your phone battery capacity, then expect only roughly two thirds of that in practice because of conversion losses. A 10,000mAh bank typically gives a bit over one full charge to a large phone battery.
Can I take a power bank on a plane?
Power banks must go in hand luggage, not checked baggage. Most airlines allow up to 100Wh without approval. Larger ones may need airline approval. Always check your own airline's rules.
Does fast charging damage my battery?
Modern phones manage charging speed and heat. Heat is the main enemy of battery life, so avoid charging under pillows or in hot cars, and use a good quality charger and cable.
Do I need a GaN charger?
GaN chargers are smaller and run cooler for the same power. They are a nice upgrade for travel, but not essential for everyday use.
How we write our guides: they explain what to look for, based on general knowledge and published guidance. We have not tested every product mentioned, and prices and availability change. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. See our Editorial Guidelines and Affiliate Disclosure.
