Question about ETL and UL Certifications for battery powered tools
Due diligence with appropriate certification test reports are necessary for hazardous goods like LiPo packs with all the UN 38.3 test requirements set forth by United Nations.

read http://www.batteryuniversity.com/learn/article/building_a_lithium_ion_pack

Even if shipped by sea, there are risks to damage and supplier packaging test reports must include 1.2m drop tests on all sides and corners.  (which may not be enough for some shippers.!)

more details https://www.law.cornell.edu/cfr/text/49/173.185

Also get the UL test report for http://industries.ul.com/consumer-technology/batteries.

I would demand an ongoing Quality reliability verification program with measurable performance and safety parameters and consider large 3rd party liability insurance costs.