How to read a battery safety rating
AIS-156 and the other marks on a pack tell you what was tested, not everything you need to know.
A safety standard is a floor, not a guarantee. Understanding what a mark covers helps a buyer ask the questions the mark does not answer.
What the standard is for
AIS-156 sets out tests for traction batteries used in electric vehicles: mechanical abuse, thermal exposure, overcharge, short circuit and related failure modes. Passing means the design survived a defined set of tests under defined conditions.
What it does not cover
- How the pack behaves after two years of vibration on a bad road.
- Whether the BMS correctly detects a sensor failure.
- Whether the assembly process is consistent from unit to unit.
- How the pack interacts with a particular charger.
Those are design and quality questions, not certification questions. A pack can pass the test and still fail in the field if its assembly is inconsistent.
The questions worth asking
- Which cells, and what is the supplier’s traceability?
- How is the pack sealed against dust and water?
- What does the BMS do when a temperature sensor fails open or short?
- How is the pack tested after assembly, and is the record kept?
- What happens to a pack that fails in service: repair, replace or recycle?
The paperwork behind the mark
Ask for the test report, not just the certificate. The report shows the conditions and the margins. A design that passed with a thin margin is a different product from one that passed comfortably.
The bottom line
Use the rating to exclude the obviously unsafe. Use the engineering questions to choose between the ones that remain.