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Building a Lithium-ion Pack
Reputable battery manufacturers do not supply lithium-ion cells to uncertified battery assemblers. This precaution is reasonable when considering the danger of explosion and fire when charging and discharging a Li-ion pack beyond safe limits without an approved protection circuit.Authorizing a battery pack for the commercial market and for air transport can cost $10,000 to $20,000. Such a high price is troubling when considering that obsolescence in the battery industry is common. Manufacturers often discontinue a cell in favor of higher capacities. The switch to the improved cell will require a new certification even though the dimensions of the new cell are the same as the previous model.
Cell manufacturers must comply with their own vigorous cell testing and we ask, “Why are additional tests required when using an approved cell?” The cell approvals cannot be transferred to the pack because the regulatory authorities do not recognize the safety confirmation of the naked cell. The finished battery must be tested separately to assure correct assembly and is registered as a standalone product.
As part of the test, the finished battery must undergo electrical and mechanical assessment to meet the Recommendations on the Transport of Dangerous Goods on lithium-ion batteries for air shipment, rules set by the United Nations (UN). The electrical test stresses the battery by applying high heat, followed by a forced charge, abnormal discharge and an electrical short. During the mechanical test, the battery is crush-tested and exposed to high impact, shock and vibration. The UN Transport test also requires altitude, thermal stability, vibration, shock, short circuit and overcharge checks. The UN Transport works in conjunction with the Federal Aviation Administration(FAA), the US Department of Transport (US DOT) and the International Air Transport Association (IATA).*
The authorized laboratory performing the tests needs 24 battery samples consisting of 12 new packs and 12 specimens that have been cycled for 50 times. IATA wants to assure that the batteries in question are airworthy and have field integrity. Cycling them for 50 times before the test satisfies this requirement.
The high certification costs make many small manufacturers shy away from using Li-ion for low-volume products; they choose nickel-based systems instead. While strict control is justified, an uncertified Li-ion kept in the hands of the expert and out of aircraft would be acceptable, but controlling such movement in the public domain is next to impossible. This makes it hard for the hobbyist who wants to win a race with a high-powered Li-ion battery but is bogged down by many rules.
With recurring accidents while transporting lithium-based batteries by air, regulatory authorities will likely tighten the shipping requirements further. However, anything made too cumbersome and difficult will entice some battery manufacturers to trick the system, defeating the very purpose of protecting the traveling public.
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