Why is there a 30% SOC limit for air transportation of lithium batteries?

This regulation was discussed and decided at the 25th meeting of the International Civil Aviation Organization Dangerous Goods Expert Committee on October 19-30, 2015. During the meeting, representatives from multiple parties had a lively discussion on this issue. The proposer of this rule pointed out that there is a significant danger in the transportation of lithium batteries, but when the battery charge SoC decreases to a lower level, it can greatly reduce the diffusion of lithium battery thermal conduction and the occurrence of dangerous accidents, effectively reducing the danger of air transportation.

For the concerns of the battery industry about the impact of self discharge of lithium batteries, it is claimed that a monthly discharge rate of 2% is a normal situation, and sufficient SoC should be maintained to meet the needs of storing lithium batteries during long transportation times. However, too low SoC will directly lead to battery degradation and damage.

The test results from multiple laboratories, including the FAA Technical Center, showed that most of the tested battery cells did not exhibit thermal conduction diffusion when the state of charge dropped to 30%. For most battery cells today, a 30% SoC is a relatively safe capacity ratio.

After heated discussions, the expert group agreed to limit SoC to 30%, which takes into account that most batteries have sufficient storage time and will not affect battery life due to self discharge. The meeting decided to include this content in the Technical Instructions for the Safety Transport of Dangerus GOODS BY AIR, 2015-2016 EDITION/ADENDUM NO. 3. This regulation has been implemented since April 1, 2016.

The requirements for the battery capacity of air freight batteries are different from those of the International Maritime Dangerous Goods Code. If batteries are transported by sea, there is no battery capacity limit requirement by now. Even so, we still recommend that sea transportation should be kept between 50% and 80% for safety.