Flying with a flashlight

Airline battery rules are written in watt-hours. That is convenient, because watt-hours is the unit this site already computes for every light it covers — and once you run the arithmetic, the answer for flashlights turns out to be reassuring in a way most travel advice never bothers to establish. The largest battery in any light we cover is 30.2 watt-hours. The limit is 100.

So the watt-hour ceiling is almost never what catches a flashlight owner. Something else is, and it catches people constantly: the rule about where a *spare* cell may travel. That distinction is the whole of this page.

The four rules that actually matter

Stripped of everything that does not apply to portable lights, current FAA and TSA guidance comes down to four statements.

1. A battery installed in a device may travel in either bag. TSA rules a lithium battery of 100 watt-hours or less, installed in a device, as permitted in both carry-on and checked baggage. A flashlight with its cell in it is a device.
2. A spare cell must travel in the cabin. FAA and TSA both state that spare, uninstalled lithium-ion and lithium metal batteries — including power banks — must be carried in carry-on baggage only, and are prohibited in checked baggage. This is the rule that catches flashlight owners.
3. Spares must be individually protected against short circuits. The FAA names three acceptable methods: leave the cell in its original retail packaging, tape over the exposed terminals, or place each cell in its own separate plastic bag.
4. Above 100 watt-hours you need permission; above 160 you cannot fly it. Batteries from 0 to 100 Wh are allowed. From 101 to 160 Wh they require the air carrier's approval, and passengers may carry at most two such spares. Above 160 Wh they are forbidden on passenger aircraft.

There is a fifth that only bites at the gate: if your carry-on bag is checked planeside or at the gate, the FAA requires that all spare lithium batteries and power banks are removed from it first and kept with you in the cabin. That is easy to forget on a full flight when the bag is taken from you at the jet bridge.

What the limit looks like against real lights

This is where the arithmetic becomes useful rather than abstract. Every light below publishes either a battery energy figure directly or a capacity we can convert, so each row is checkable rather than asserted.

Nothing is close. The largest figure on the site is the Fenix HM75R at 30.2 watt-hours, and that is a headlamp carrying two cells at once including a rear power bank. It uses under a third of the allowance. A typical rechargeable headlamp sits between 3 and 12 watt-hours, which is three to thirty times under the ceiling.

The rule that actually catches flashlight owners

It is not the ceiling. It is the spare.

Flashlight owners are unusually likely to carry loose cells, because a large part of this hobby is built on removable 18650 and 21700 batteries and the habit of carrying a charged spare. A loose 21700 rolling around in a checked bag is exactly what the rules prohibit — not because of its energy, which is trivial at 18 watt-hours, but because an uninstalled cell can short against keys, coins or another cell in a bag nobody can reach at 35,000 feet.

• Light with the cell installed — either bag. Put it in the carry-on anyway; you will want it if the power goes out in a strange hotel.
• Spare cells, of any size — cabin only, every time, with the terminals protected.
• A headlamp with a sealed built-in battery — a device, so either bag. There is nothing to remove.
• A power bank, including a headlamp that doubles as one — treated as a spare battery. Cabin only.

Lithium primaries and ordinary alkalines

Two of the cell types this site covers most often are not lithium-ion at all, and they are governed differently.

CR123A and lithium AA primaries are lithium metal cells, and those are rated by lithium content in grams rather than in watt-hours. The FAA limit is 2 grams of lithium per battery for ordinary carriage, with 2 to 8 grams possible only with airline approval. Consumer CR123A and lithium AA cells of the kind that go in a Streamlight PolyTac or a ProTac HL-X sit well inside the 2 gram class. They are still spares when they are loose, so the cabin-only rule applies to them exactly as it does to a 21700.

Ordinary alkaline AA and AAA cells are not lithium at all and are not covered by any of the lithium rules. This is the quietest argument for an alkaline light as a travel light, and it is the reason the first pick on this page runs on a single AA.

The disclosure problem, in a place you can feel it

Here is where this site's usual complaint stops being academic. Most flashlight makers do not publish battery capacity at all. Across the lights we cover, only Fenix and Petzl state a capacity or a watt-hour figure. Nitecore, Olight, Coast, Black Diamond, Klein, Nebo, Astro and Streamlight do not, on the pages available to us.

For nearly all travel that costs you nothing, because a light with a sealed cell is a device and no one asks. But if you are ever questioned about a spare, or you are flying a carrier with its own stricter policy, the ability to point at a printed watt-hour figure is worth something — and with most brands you simply do not have one. A specification you cannot cite is a specification you do not really have.

Four lights, four travel situations

Acebeam Pokelit AA — the version of this problem that does not exist

550 lumens from a single AA cell, at CRI 90 or better with IP68. Run it on an ordinary alkaline and none of the lithium rules on this page apply to you at all: no watt-hour figure to know, no spare-battery rule, no terminal taping. For a traveler who wants to stop thinking about this entirely, that is the answer. The cons are real — Acebeam publishes no runtime, and 550 lumens is a task light rather than a search light.

Petzl Actik Core — the best-documented case

625 lumens with a published 4.5 Wh CORE pack, and it also runs on three AAA cells. That hybrid is the ideal travel arrangement: fly on AAA if you would rather not think about it, use the rechargeable pack the rest of the time, and if anybody ever asks what is in it, Petzl prints the number. Petzl is one of only two brands we cover that publishes battery energy directly. Cons: IPX4 only, so rain but not immersion, and 88 g is not the lightest lamp in its class.

Streamlight MacroStream — the sealed-cell case, honestly flagged

500 lumens, 2,000 candela, 90 m, 62.4 g, and a built-in cell that charges over USB. As a device it travels in either bag with nothing to remove, which makes it genuinely easy to fly with. The honest catch is that Streamlight does not publish the capacity, so we cannot tell you its watt-hours and neither can you. It is certainly far under 100 Wh given the size, but that is an inference rather than a citation. Cons: IPX4, and 8 hours on low is the shortest runtime among our picks.

Fenix PD36R Pro — the one where the spare rule bites

2,800 lumens, 380 m and the largest single cell on this site at 5,000 mAh, or 18.0 watt-hours computed. It is the best light of the four by some distance and the one that demands you actually follow the rule: if you carry the charged spare 21700 that makes this light worth owning, it goes in the cabin with its terminals covered, never in the hold. Cons: at 169 g it is large for a travel light, and Fenix publishes only a single maximum runtime rather than a per-mode table.

A packing checklist

1. Put the light in your carry-on with its cell installed. It is permitted in either bag, and a light in the hold is a light you cannot reach.
2. Take every loose cell out of your checked bag. This is the only rule on this page that people routinely break.
3. Protect each spare — retail packaging, taped terminals, or one cell per plastic bag.
4. Check your own light's watt-hours if the maker publishes a capacity. Almost certainly under 20 Wh, and the ceiling is 100.
5. If your bag gets gate-checked, pull the spares and the power bank out before you hand it over.
6. Check your airline's own policy, which may be stricter than the FAA's, especially on power banks.

What we would not tell you

We would not tell you your specific airline's policy, because carriers set their own and several are stricter than the regulator — particularly on power banks, where limits on the number carried have been tightening. We link the FAA and TSA pages below so you can read the current text yourself rather than trusting a summary that may have aged.

We would also not tell you the watt-hours of a light whose maker does not publish a capacity. For the Streamlight MacroStream above we can reason that a cell that size is nowhere near the limit, and we still will not print a number, because an inference in a table looks exactly like a measurement and it is not one.