Battery and cell supply
Battery capacity is part of your specification, and so is the cell. Agree who sources the cells, who qualifies an alternative cell if supply tightens, and who holds the transport documentation. For air transport, every lithium cell and battery type must have passed the applicable tests in subsection 38.3 of the UN Manual of Tests and Criteria, and the manufacturer and later distributors must make the test summary available. Ask for it before the first shipment, not after.