The US Postal Service has changed standards for mailing batteries. The final rule sets a five-pound maximum mail piece weight limit when primary lithium and lithium-ion batteries are not packed with or installed in the devices they operate.
There is an 11-pound mail piece weight limit when batteries are packed with or installed in the device they operate. The rule allows for batteries packed directly by the retailer or another source. The USPS requires a Surface Mail Only label as well; beginning January 1, the US Department of Transportation will require an additional Primary Lithium Batteries - Forbidden for Transportation Aboard Passenger Aircraft label.