Can You Fly With the Power Bank From Your Mystery Box?
A power bank turns up in many electronics mystery boxes, though never in a Mewoo one, and it is one of the few items that airport security cares about. You cannot put it in checked luggage, some sizes need the airline's permission, and a few airlines now tell you where it must sit during the flight. Here is what you need to check on the power bank from your box before you pack it.
Carry-On Only, Every Time
The rule that matters most is the simplest. In the United States, the Federal Aviation Administration treats a power bank as a spare lithium battery, and spare lithium batteries are not allowed in checked baggage. They go in the cabin with you. If your carry-on is taken from you at the gate and put in the hold, you are expected to take the power bank out first and keep it on you. The reasoning is that a battery fire in the cabin can be seen and dealt with, and one in the hold cannot.
That rule has no size threshold. A tiny 5,000mAh stick and a large 20,000mAh brick are both cabin-only. Most other countries apply the same principle, because it comes from the international dangerous goods rules that airlines everywhere follow. The chemistry behind the rule, and why it also shapes how a box is shipped to you in the first place, is in why lithium batteries decide what can be in your electronics box.
The 100 Watt-Hour Line
- Power banks are cabin-only in the US and almost everywhere else; never put one in checked luggage.
- Up to 100Wh you need no approval; from 101 to 160Wh you need the airline's permission and are limited to two; above 160Wh the bank cannot fly.
- Convert mAh to Wh by dividing by 1,000 and multiplying by 3.7; if the bank prints no capacity at all, leave it at home.
Size is measured in watt-hours, not the milliamp-hours printed in large type on the case. The FAA's limits are these. Up to 100Wh, you can carry the bank without asking anyone. From 101 to 160Wh, you need the airline's approval and can carry no more than two. Above 160Wh, the bank does not fly at all, in the cabin or the hold.
Most power banks print the watt-hour figure somewhere in small type. If yours prints only mAh, you convert it. Take the mAh, divide by 1,000, and multiply by the cell voltage, which for almost every power bank is 3.7 volts. A 10,000mAh bank is 37Wh. A 20,000mAh bank is 74Wh. A 27,000mAh bank is almost exactly 100Wh, and anything larger than that crosses the line where you have to ask.
The number the rule cares about is the one printed on the bank. If the bank prints nothing at all, no Wh, no mAh, no voltage, security can refuse it, and some airlines instruct their staff to do exactly that. An unmarked bank is a bank you use at home.
Where It Sits During the Flight
Until recently, once the bank was in your cabin bag nobody cared where it went. That has changed. In 2025 a series of cabin fires traced to power banks led several airlines, first in Asia and then elsewhere, to add rules about use on board. Some now forbid charging from a power bank during the flight. Some forbid putting one in the overhead bin. Southwest, from late May 2025, requires that a power bank in use be kept in plain sight, not inside a bag or the bin. Other carriers have followed with their own versions.
You should treat those rules as airline-specific and check them the week you fly, because they are still being written. The safe habit that satisfies all of them is simple: keep the bank in the seat pocket or your lap, use it only if your airline allows it, and never leave it charging in a bag you cannot see.
Quick Reference
| Printed capacity | Watt-hours | Checked bag | Cabin | Approval needed |
|---|---|---|---|---|
| 5,000mAh | 18.5Wh | No | Yes | No |
| 10,000mAh | 37Wh | No | Yes | No |
| 20,000mAh | 74Wh | No | Yes | No |
| 27,000mAh | 100Wh | No | Yes | No |
| 30,000mAh | 111Wh | No | Yes, max two | Yes, from the airline |
| 43,000mAh and above | 160Wh+ | No | No | Not permitted |
| Nothing printed | Unknown | No | May be refused | Leave it at home |
Read the table against the bank in your hand, not against the box it came in. Some cheap banks print a capacity on the packaging and a different one on the case, and the case is what security reads. Some print a figure that is simply not true, which is a separate problem covered later. For flying, the printed number is what you are held to.
Note: Protect the ports. The FAA asks you to prevent short circuits on spare batteries, and for a power bank that means keeping its USB ports away from keys, coins and other metal in your bag. A small pouch, or the original packaging, is enough. A bank that has been crushed, swollen or dropped hard should not fly at all; the same goes for one that gets warm when idle.
What About the Cable and the Charger?
The cable and the wall charger that may have come with the bank have no battery in them and no flight rule attached. They can go in either bag. What is worth checking before you rely on them abroad is whether the charger accepts the local voltage and the cable can carry what the bank puts out. Those are separate questions, answered in will the electronics in your mystery box work on your voltage and how to read the USB cables in your mystery box.
Before You Pack: A Two-Minute Check
- Find the Wh figure on the bank itself. If only mAh is printed, convert it and write the Wh on a piece of tape on the case.
- Confirm it is 100Wh or under. If it is between 101 and 160, email or message the airline before you travel and keep the reply.
- Check your airline's in-flight use rule for the week you fly.
- Put it in your cabin bag, ports covered, where you can reach it if the bag is gate-checked.
- Charge it at home so you are not depending on using it in the air.
If any step fails, the bank stays home. A power bank is cheap; a delay at security is not.
Is the Printed Capacity True?
For flying, the printed figure is what counts. For your own use, it may not be what you get. Inexpensive banks often deliver noticeably less than the label, partly because conversion from 3.7V cells to 5V output loses some energy, and partly because some labels are simply optimistic. A 10,000mAh bank that charges a phone with a 4,500mAh battery about one and a half times is behaving normally. One that manages a single half charge is either mislabelled or worn, and that is something to test inside the seller's window rather than discover on a trip. A bank with a solar panel on the front follows the same flight rules and adds a slower question, answered in solar power banks in a mystery box. The routine for checking what arrived is in how to document a mystery box on arrival.
What This Means When You Order
Mewoo does not put a power bank in any box: it is the item carriers most often refuse on international post, and the reasons are in why lithium batteries decide what can be in your electronics box. So the bank you are packing came from another seller's box or your own drawer, and the rules above apply to it all the same. If a seller does include them, ask whether the bank carries a printed Wh or mAh figure and a maker's name, because an unmarked bank is useless for travel and hard to trust at home. Then do the two-minute check, keep it in the cabin, and it will fly as far as you do.
FAQ
Can I put a power bank in checked luggage?
No. Airlines classify it as a loose lithium battery, and loose lithium batteries are banned from the hold worldwide because a fire down there cannot be reached. Carry it in the cabin, and if staff take your bag at the aircraft door, pull the bank out before handing the bag over. This applies to the smallest stick charger as much as to a large brick.
How do I work out the watt-hours of my power bank?
Turn the big number into thousands, then scale it by the cell voltage. A bank labelled 20,000mAh is 20 thousand; 20 times 3.7 gives 74Wh. If the label shows a voltage other than 3.7, use that instead. Many cases already carry the Wh figure in tiny print underneath, so look there first. Whatever you calculate, the moment questions start at security is when the total passes 100.
What happens if my power bank has no capacity printed on it?
Expect it to be confiscated. Screening staff cannot verify a limit they cannot read, and airline guidance increasingly tells them to refuse unlabelled batteries rather than guess. Cheap banks from any source, mystery boxes included, sometimes arrive this way. Keep such a bank for home use and travel with one that carries a maker's name and a clear Wh or mAh marking.
Can I use the power bank during the flight?
It depends on the airline, and the answer changed for many carriers during 2025. Some now ban charging from a bank in the air; others allow it only if the bank stays visible in your lap or seat pocket rather than in a bag. Look up your specific airline's rule in the days before departure, and when in doubt charge your phone from the seat's USB port instead.
Is a 20,000mAh power bank allowed on a plane?
Yes, and nobody needs to sign anything. Its energy works out around three quarters of the threshold at which permission becomes necessary, so it travels as freely as a phone provided it rides in the cabin with its sockets shielded. Trouble begins in the high twenty-thousands, where approval and a two-bank cap kick in, and stops altogether in the low forty-thousands, where no airline will accept it.
The power bank from my box gets warm while it is not in use. Is that safe?
Treat it as suspect. A healthy bank stays at room temperature when idle; warmth with nothing connected suggests an internal fault, and a swollen case or a bank that was dropped hard belongs in the same category. Do not fly with it and do not charge it unattended. Photograph it, report it to the seller inside the faults window, and dispose of it through a battery recycling point.
Final Thoughts
A power bank flies in the cabin or not at all. Under 100Wh you need no permission; 101 to 160Wh needs the airline's approval and a limit of two; above that it stays home, as does any bank with no capacity printed on it. Convert mAh to Wh with the 3.7 rule, cover the ports, check your airline's in-flight rule the week you travel, and the power bank from your box will pass security as easily as your phone.
If you would rather have a box of the small rechargeable items that pass security without a question, earbuds, watches and speakers, powered on before dispatch, start with the Triple Reveal Electronics Mystery Box (3 items) or the Party Electronics Mystery Box (6 items). Compare every tier side by side on the electronics mystery box category page.
See how boxes are packed and shipped →
