Standalone lithium in the mail rides in trucks. Air is off the table.
The short answer, chemistry by chemistry
| Chemistry | In the mail? | What the box needs |
|---|---|---|
| Alkaline (AA, AAA, C, D, 9 V) | Yes, domestic and international, any class | Terminals covered; cells packed so they cannot short against metal or each other |
| NiMH and NiCad rechargeable | Yes, treated the same as alkaline | Terminals covered; no loose cells rolling around |
| Lithium-ion cell (single) | Yes, up to 20 Wh per cell | Ground surface only when standalone; the lithium battery mark and Surface Mail Only text |
| Lithium-ion battery pack | Yes, up to 100 Wh per battery | Same ground and marking rules; a 5-pound mailpiece ceiling for standalone batteries |
| Lithium metal (primary) | Yes, up to 1 g per cell and 2 g per battery | Standalone are surface only; installed in equipment can go by air under the small-battery relief |
| Damaged, defective or recalled lithium | No, never | USPS refuses these outright. A hazmat-trained shipper is the only lane |
Everything above the lithium line is straightforward: cover the terminals, pack the cells so nothing can rub metal, print a label, hand it over. The interesting rules all start with lithium.
Lithium in the mail, in three numbers
Publication 52 sets three ceilings for lithium in domestic mail. Miss any of them and the box either does not fit the postal lane or has to be tendered a different way.
20 Wh per cell, 100 Wh per battery
The watt-hour rating is on the label of every consumer lithium-ion cell and battery pack. A phone battery is well under 20 Wh; a laptop pack sits at 40 to 90 Wh; an e-bike or hoverboard pack blows past 100 Wh and cannot go through the mail as a standalone battery at all.
5 pounds per package, standalone
The whole mailpiece is capped at 5 pounds when the box holds lithium batteries by themselves. That covers a spare laptop pack in bubble wrap; it does not cover a case of them. Devices with the battery installed are held to different weight rules.
Surface only, air prohibited
A standalone lithium-ion or lithium-metal cell in the mail rides in a truck, never a plane. USPS Ground Advantage and USPS Parcel Select are the classes that carry them. Priority Mail Express and international air mail are off the table.
A very small exception exists for the button-cell class. Lithium-ion cells or batteries at 2.7 Wh or less, and lithium-metal cells at 0.3 grams of lithium or less, may travel installed in equipment by air with a 5.5-pound mailpiece ceiling. That is the relief that keeps a smartwatch or a hearing aid mailable by any class.
What has to be on the box
The lithium battery mark itself is the standard yellow-and-red rectangle with the four-digit UN number and a phone number for hazmat information. The 2015 update matched the UN numbers postal customers write: UN3480 for standalone lithium-ion, UN3481 for lithium-ion packed with or installed in equipment, UN3090 for standalone lithium metal, and UN3091 for lithium metal with equipment. Standalone shipments carry the extra line reading Surface Mail Only, Secondary Lithium Batteries — Forbidden for Transportation Aboard Passenger Aircraft (or Primary Lithium Batteries on the metal-cell version). Neither line is optional; a package without both is a mailpiece the acceptance clerk is instructed to refuse.
Installed batteries carry a smaller burden. A phone in its box needs the same terminal protection any consumer would use, the mailpiece has to be marked appropriately, and the mailer is expected to know the battery is inside — but the delivery lane is the same one carrying a birthday card.
The international line
USPS international mail is stricter than the domestic side, and lithium is where the difference bites. Standalone lithium batteries cannot go abroad in the mail at all, in any class, to any country. Only the small-consumer-battery relief applies: a lithium cell installed inside the equipment it powers, at 20 Wh or less per cell, with the mailpiece properly declared. That covers a phone, a camera, a hearing aid, a watch. It does not cover a spare pack in the same box.
The APO, FPO and DPO military system is treated as international for battery purposes. The same install-only relief applies, and the same standalone prohibition. A soldier's spare drone battery cannot be mailed through the military system in the way a spare drone can.
Where these rules come from
- USPS Postal Explorer, Publication 52 Section 349, Class 9 Hazardous Materials, and Appendix C Packaging Instruction 9D. Read 2026-08-11.
- USPS About, Publication 52 Revision, March 2 2015 — the watt-hour caps, the 5-pound standalone ceiling, and the small-battery air-eligibility relief. Read 2026-08-11.
- USPS Shipping Restrictions, lithium battery notice — the Restricted Electronic Device and Surface Transportation Only marks for used or refurbished devices. Read 2026-08-11.
USPS revises Publication 52 without notice, and the DOT hazmat regulations behind it change on a separate schedule. The figures above are what USPS published on the date shown; a mailer at scale should read the current text before printing labels.
Common questions
Can you send AA or AAA batteries by USPS?
Yes. Alkaline, NiMH and other non-lithium consumer cells are ordinary mail, domestic or international, so long as terminals are covered and cells cannot short against each other.
What is the USPS watt-hour cap on a lithium-ion battery?
Publication 52 Packaging Instruction 9D caps a lithium-ion cell at 20 Wh and a full battery at 100 Wh. Anything over those numbers cannot go through the mail at all.
Can standalone lithium batteries ship USPS?
Only by surface transport, only domestically, only up to a 5-pound package, and only with the lithium battery mark plus the words Surface Mail Only on the box. USPS Ground Advantage is the mail class that carries them.
Can I mail lithium batteries internationally with USPS?
Only when the battery is installed inside the equipment it powers, and only under the small-consumer-battery relief. Standalone lithium batteries are prohibited from international mail entirely.
Which USPS services can carry lithium batteries?
USPS Ground Advantage and USPS Parcel Select for standalone batteries; Priority Mail is allowed for devices with installed batteries under the small-battery relief. Priority Mail Express and international air mail are off the table for standalone lithium cells.