Travel routers and power banks for long train days: what to check before you buy

A long train day is the best part of a trip until your phone hits 12% somewhere between two stations and the seat has no outlet. See also the tech gear guides and the broader gear section. Items are described by type while partner links are set up, and price tiers are a rough guide only: $ is the lowest and $$$ the highest for that type. Read the live listing before you buy, and see how we make money for how partner links work.

The short version: almost everyone benefits from a power bank, and far fewer people need a router.

The number on the box is mAh, but the number that matters for flying is watt-hours (Wh). Wh equals capacity in mAh multiplied by voltage, divided by 1,000. At a typical 3.7 V cell voltage, a 10,000 mAh bank works out to 37 Wh and a 20,000 mAh bank to 74 Wh. Many banks print the Wh figure on the case, and if yours does, trust that number over the arithmetic.

Three more facts help you read a product page. First, a bank never delivers its full rated capacity to your phone, because voltage conversion and heat use some of it. Compare banks by Wh and by the maker's stated output, and keep your expectations modest. Second, output wattage decides what you can charge. A phone is happy with a modest USB-C port, while a laptop needs a higher-wattage USB-C port and a bank designed to deliver it, so check your laptop charger's rating before you shop. Third, ports often share power. A bank with a high-wattage port may drop to a lower output when two devices are plugged in, so the manufacturer's note on multi-port output matters.

Other details worth checking are weight, recharge time, whether the bank can charge while it charges your phone, and whether the Wh rating is printed on the product, not just in the box.

A phone-class bank is a good choice for one phone and nothing else. It is small enough for a jacket pocket and light enough that you will actually carry it. It will not charge a laptop in any useful way, and a single port means no charging two devices at once.

A mid-size USB-C bank is the safest choice for most travelers who spend whole days on trains and use the phone for maps, tickets and photos. It gives you several phone charges and can top up a laptop if it has a suitable USB-C port. It is heavier, so decide whether you will use that capacity. At about 74 Wh for a typical 20,000 mAh bank, it still sits under the 100 Wh line most airlines use.

A large high-wattage bank suits people who work from a seat with no outlet. The catch is airline rules. A bank near 100 Wh is the one most likely to be asked about at security, and a bank above 100 Wh needs the airline's approval, with 160 Wh as the ceiling. For the reasons below, treat a bank above 100 Wh as a special case, not a default.

A travel router connects to one network, such as hotel Wi-Fi or a wired port, and makes your own private Wi-Fi from it. That is useful in three situations. You have several devices that would each need to log in to hotel Wi-Fi. The room has an Ethernet port and no Wi-Fi. Or you want a VPN running for every device at once.

It is not useful in several others. A router cannot make a slow connection faster, so on a train with slow or capped onboard Wi-Fi it only passes on the same limits. If you already have an eSIM with enough data, your phone's hotspot can share it with a laptop, which solves the same problem with nothing extra to carry. Read the eSIM options for Japan and the wider connectivity guides before you add another device to your bag.

On a router's product page, check these:

• Power source. A router that runs from USB-C can share a power bank, but it is one more draw on the battery.

• Ports. An Ethernet port matters if you stay in places with wired internet.

• Captive portal support. Hotel networks often use a login page. Look for the maker's documentation on how the router handles it, and for whether setup works from a browser or only an app.

• VPN support. If you need it, confirm which protocols the router supports.

• Wi-Fi standard and size. Newer standards help when many devices share the link, and a smaller router is easier to carry.

• Setup requirements. Check what the app asks for before you install it.

A mobile router with a SIM slot is a different product. It makes its own connection from mobile data, which suits groups who want to share one data plan or families where not every phone supports an eSIM. Check which bands it supports in the country you are visiting, whether it is locked to a carrier and the battery life as claimed by the maker, bearing in mind that a claim is not a measurement. For one or two people, an eSIM and a hotspot do the same job with less to carry.

Airlines follow the international rules, and those changed this year. On 27 March 2026 ICAO issued an addendum to its Technical Instructions on power banks. IATA's guidance for operators, dated 31 March 2026, summarizes the requirements for passengers:

• Power banks must be carried as carry-on baggage and are not allowed in checked baggage.

• No more than two power banks may be carried per person.

• A power bank must not be recharged while on board the aircraft.

• A power bank should not be used to recharge a device while on board.

• Each power bank must be individually protected against short circuits.

IATA's table shows that banks of 100 Wh or less need no operator approval, banks from 100 to 160 Wh need the airline's approval, and banks above 160 Wh are forbidden. IATA also says the option to carry 100 to 160 Wh banks with approval will not carry into the 68th edition of its regulations that takes effect on 1 January 2027, and that it has been communicated in guidance this year to manage passenger expectations. In practice, keep every bank at 100 Wh or less.

Individual airlines add their own conditions. Ryanair's terms, for example, say power banks must be carried on your person or in the bag under the seat in front, not in overhead lockers, and that batteries above 100 Wh are not permitted.

Japan has its own measures. JNTO's notice, based on a Japanese transport ministry press release, says that from 24 April 2026 a maximum of two power banks of 160 Wh or less may be carried, charging a power bank on board is not permitted and using one to charge other devices on board is not permitted. The ministry's leaflet, which JNTO links, also asks passengers not to put power banks in overhead compartments, to protect each terminal against short circuits and to keep the bank in a seat pocket or similar place close to them. Some airlines may apply stricter rules. Because these rules are moving, check the page of every airline on your route in the week you fly.

Do not count on a socket. SmartEX, the reservation service for the Tokaido, Sanyo and Kyushu Shinkansen, says that on the N700, N700A and N700S trains all Green Car seats have power outlets, and in ordinary cars the window seats and the seats at the front and rear have them. JNTO also notes that newer shinkansen have outlets next to the window seats and suggests asking the staff for such a seat when you buy your ticket. Older trains and many regional trains elsewhere may have fewer sockets, so a power bank is the safe choice on a rural route.

A sensible day kit is a power bank, one short USB-C cable, a second cable for your phone if it is not USB-C, and a two-port USB-C charger with a plug adapter for the country. Leave the router at the hotel on train days, because onboard Wi-Fi is the weak link that a router cannot fix. A phone with an eSIM and a hotspot is usually enough. Download maps and tickets before you leave the hotel, because signal drops in valleys and tunnels.

JNTO states that Japan's voltage is 100 V, with 50 Hz in eastern Japan and 60 Hz in western Japan. Japan's outlets take flat two-pin plugs. Many phone and laptop chargers accept a range of voltages, so check the small print on each brick, and bring an adapter if your plugs are a different shape. JNTO also notes that some appliances, such as hair dryers and shavers, may need a step-down transformer if they are not dual voltage.

The most common mistake is buying on mAh alone. Check the Wh figure, the output wattage and whether the product states them clearly. The second is packing a power bank in checked baggage, which is not allowed. The third is carrying more than two. The fourth is assuming an airline's rule matches the international minimum, when some add conditions about overhead bins or in-flight use.

Other mistakes are quieter. Buying a router when an eSIM hotspot would do. Expecting a router to fix train Wi-Fi. Leaving a power bank in a coat you hand to someone else. And forgetting that the bank itself needs charging, which is easy to do after a day of travel and a long dinner.

Most travelers do not need a travel router. If you have an eSIM with enough data, your phone's hotspot covers a laptop, and hotel Wi-Fi is fine for one or two devices that each log in once. Buy a router only if you regularly have several devices on one hotel connection, want a VPN for everything, or stay in places with wired internet.

For power banks, the case is narrower. On trips where you are back at the hotel every evening and your phone lasts a day, you may not need one. If your days are long and your route is rural, carry one. For a full packing list that includes a power bank, see what to pack for Japan in spring, and for route ideas that make use of slow trains, see Tohoku by local train.