UN 38.3 (lithium battery transport testing)

Section 38.3 of the UN Manual of Tests and Criteria defines eight tests for lithium cells and batteries: altitude simulation, thermal cycling, vibration, shock, external short circuit, impact or crush, overcharge and forced discharge (some apply only to cells). A test summary must be made available by manufacturers and subsequent distributors; without it, carriers and freight forwarders will refuse shipments.

Passing the tests is not the whole story. Shipping rules depend on configuration (batteries alone, such as lithium-ion under UN 3480; packed with or contained in equipment under UN 3481) with packaging, labeling and state-of-charge requirements that vary by transport mode, air being the strictest.

Where it bites: buying cells that passed UN 38.3 doesn't cover your custom pack; a new pack design needs its own testing, which takes time and samples. Late battery changes can hold up shipments.