I am pretty certain he's just plain wrong.
DMM Postal Regulations on mailing rechargeable batteries
10.20.6 Secondary Lithium-ion (Rechargeable) Cells and Batteries
Small consumer-type lithium-ion cells and batteries like those used to power cell phones and laptop computers are mailable domestically under the following conditions. There are unique standards and limits when mailing primary lithium cells or lithium batteries internationally, or to and from an APO, FPO, or DPO destinations. See IMM 136 for details.
a. General. The following additional restrictions apply to the mailability of all secondary (rechargeable) lithium-ion cells and batteries:
1. The lithium content must not exceed 20 Wh (Watt-hour rating) per cell.
2. The total aggregate lithium content must not exceed 100 Wh per battery.
3. Each cell or battery must meet the requirements of each test in the UN Manual of Tests and Criteria, Part III, and subsection 38.3 as referenced in DOTs hazardous materials regulation at 49 CFR 171.7.
4. The mailpiece must not contain more than three batteries.
5. All outer packages must have a complete delivery and return address.
b. Installed In Equipment. The following additional restrictions apply to the mailing of secondary cells or batteries properly installed in equipment they operate:
1. The batteries installed in the equipment must be protected from damage and short circuit.
2. The equipment must be equipped with an effective means of preventing it from being turned on or activated.
3. The equipment must be cushioned to prevent movement or damage and be contained in a strong enough sealed package to prevent crushing of the package or exposure of the contents during normal handling in the mail. The shipment must be mailed in a strong outer package.
c. Mailed With Equipment. The following additional restrictions apply to the mailing of secondary cells or batteries shipped with (but not installed in) the device or equipment being mailed:
1. The shipment cannot contain more batteries than the number needed to operate the device, up to three batteries.
2. The secondary lithium cells and batteries must be packaged separately and cushioned to prevent movement or damage.
3. The shipment must be contained in a strong enough sealed package to prevent crushing of the package or exposure of the contents during normal handling in the mail.
4. The outside of the package must be marked on the address side “Package Contains Lithium-ion Batteries (no lithium metal).�?
d. Mailed Without Equipment. The following additional restrictions apply to the mailing of secondary cells or batteries without equipment:
1. The secondary lithium cells and batteries must be mailed in “the originally sealed packaging�? and no more than three batteries.
2. The sealed packages of batteries must be separated and cushioned to prevent short circuit, movement, or damage.
3. The shipment must be contained in a strong enough sealed package to prevent crushing of the package or exposure of the contents during normal handling in the mail.
4. The outside of the package must be marked on the address side “Package Contains Lithium-ion Batteries (no lithium metal).�?
10.20.7 Damaged or Recalled Batteries
Damaged or recalled batteries are prohibited from mailing unless approved by the manager, Product Classification.
10.20.8 Lithium Battery Mailability
To determine the mailability of primary (nonrechargeable) lithium metal and lithium alloy batteries, or secondary lithium-ion batteries, see exhibit below. For detailed information refer to 10.20.5 and 10.20.6 respectively.
