Lithium Battery State-of-Charge Limit Explained (PI 965 Section II)

Since 1 April 2016, standalone lithium-ion cells and batteries (UN3480) shipped by air under IATA Packing Instruction 965 must be offered at a state of charge no greater than 30% of their rated design capacity. The rule came from ICAO, applies in every IATA edition since, and shows no sign of loosening. This post is the focused explainer.

Where the rule comes from

Between 2006 and 2015 there were several documented in-flight cargo fires linked to lithium-ion battery thermal runaway. The FAA Technical Center ran a series of tests showing that the heat release of a single 18650 cell in thermal runaway is dramatically lower at 30% SoC than at 50% or 100%, and that propagation between cells in a closed package is correspondingly slower.

ICAO's Dangerous Goods Panel (DGP) recommended a 30% SoC limit on the basis of those tests. It was incorporated into the ICAO Technical Instructions for the 2015–2016 cycle and into IATA DGR from the 57th edition (2016). It has been there ever since.

What exactly is restricted

• UN3480 / PI 965 — standalone lithium-ion cells and batteries shipped by air. Yes, restricted.
• UN3481 / PI 966 (lithium-ion packed with equipment) and PI 967 (contained in equipment) — the SoC rule does not apply at the IATA level. Several operators apply it voluntarily.
• UN3090 / PI 968 and UN3091 / PI 969–970 (lithium metal) — not subject to a SoC limit (lithium metal is non-rechargeable, so the concept does not apply).

Standalone lithium-ion shipped under PI 965 Section II is also forbidden on passenger aircraft entirely. Cargo aircraft only. The SoC limit applies on top of that.

How to comply in practice

1. Discharge at end of line. The cleanest answer: the manufacturer brings cells off the formation cycle to ≤30% before packaging.
2. Document and certify. The shipper must be able to show — at acceptance — that the cells comply. Many operators now require a written shipper attestation; some accept a manufacturer declaration on the commercial invoice.
3. Re-test before re-shipment. If batteries have sat in inventory under conditions that allow self-discharge, you may assume they are within limit, but if they have been on a charger (e.g. for a service or refurbishment workflow) you must re-verify.
4. Don't mix high-SoC and low-SoC cells in the same package. Compliance is per-cell, not per-package average.

How carriers verify

At acceptance, a carrier may take random samples and measure the open-circuit voltage of cells, comparing against the manufacturer's SoC-vs-OCV curve. For lithium-ion chemistries the relationship is well characterised: a typical NMC cell at 30% SoC sits around 3.6 V OCV. Carriers do not need to dismantle a battery pack — surface measurement on accessible terminals is sufficient.

Penalty exposure

SoC violations are treated as misdeclarations under most operator regimes, which means the consignment is rejected at minimum and the shipper can be referred to the regulator. PHMSA penalty exposure for a misdeclared lithium-ion shipment runs into five figures quickly. See common hazmat shipping mistakes that cost $25,000+ for the broader pattern.

For the complete lithium battery story — UN numbers, packing instructions, marks, labels, documentation — see the lithium battery shipping compliance guide. For the structural background see the complete guide to UN numbers and hazard classes.