AIS-156 Amendment 3: battery pack tests for Indian EV makers

In short

AIS-156 Amendment 3 (September 2022) phased in L-category battery rules: pack traceability from 1 Dec 2022, thermal propagation test and four sensors from 31 Mar 2023 (ARAI).

If you make electric two-wheelers, three-wheelers or the battery packs that go in them, AIS-156 is the standard your pack is tested against. Amendment 3, issued in September 2022, is the one that added the thermal propagation test and a list of pack design rules. This page walks through what the amendment text asks for, which parts came in first, and what to prepare before a test agency looks at your pack. It works from the amendment text itself, and our earlier page on AIS-156 firmware and thermal monitoring covers the telemetry side.

1. What AIS-156 and Amendment 3 cover

AIS-156 is titled "Specific Requirements for L Category Electric Power Train Vehicles". L category means motor vehicles with fewer than four wheels, plus quadricycles. The standard sets safety rules for the electric power train and for the rechargeable electrical energy storage system (REESS), which is the battery pack.

The amendment text is headed "Amendment 3 to AIS-156 (09/2022)". The Ministry of Road Transport and Highways (MoRTH) notification came on 27 September 2022. The rules were first due on 1 October 2022. EV firms were given an extension, and MoRTH split the date in two, according to an ARAI guide dated 28 September 2022:

Phase 1, from 1 December 2022: traceability of packs, an additional safety fuse, protection against regenerative braking, cell-to-cell spacing, and a microprocessor-based BMS with all protections.
Phase 2, from 31 March 2023: an earth-leakage detection charger, EMC testing of the BMS, cell testing to IS 16893 at a NABL-accredited lab, the thermal propagation test, an audio-visual warning for a thermal event, four temperature sensors in the BMS, and active parallel circuits.

Both dates are past, so a pack submitted today should be built to the whole amendment unless a later notice says otherwise.

2. BMS and charger rules (clause 6.1)

The amendment replaces clause 6.1 with these points.

Water ingress: the REESS at 100% state of charge is tested to IP X7 under IEC 60529, and there must be no fire or explosion.
BMS design: it must be a microprocessor or microcontroller circuit and meet EMC requirements under AIS 004 Part 3 at the level of the electronic sub-assembly.
BMS protections verified in testing: over-charge, over-discharge, over-temperature, overcurrent and short circuit.
Charger: charge voltage cut-off, soft start, pre-charge to detect deep discharge, protection against input supply variation of 230 VAC +/- 10%, earth leakage detection to Class 1 of IS 12640 Part I:2016, and communication with the BMS.

3. The thermal propagation test (clause 6.11 and Annex 8J)

This is the test most teams worry about. Its purpose, in the text, is to show that a short circuit inside one cell that leads to thermal runaway does not spread to the pack and cause fire or explosion.

Before the test, the REESS manufacturer has to submit three documents:

A risk reduction analysis using an industry method such as IEC 61508, MIL-STD 882E, ISO 26262, AIAG DFMEA or SAE J2929.
A system diagram of the parts that protect the user and bystanders.
A diagram showing how those parts work and which risk-reduction functions they provide.

Pass criteria. No evidence of fire or explosion triggered by a single cell thermal runaway, and an audio-visual warning that goes off at least 5 minutes before fire or explosion would occur.

How it is run. The annex uses a heater to start thermal runaway in one cell. A single-cell over-charge can be used if heating is not technically possible. Key conditions:

Item	Annex 8J
Test temperature	25 +/- 2 degrees C
State of charge at start	Not less than 95%
Heater	Run at maximum power; stop at thermal runaway or when temperature passes [300 degrees C], within [30 min]
Runaway is judged when	Cell voltage drops and dT/dt reaches [1 degree C/s], or temperature passes the maker's maximum and dT/dt reaches [1 degree C/s]
Initiation cell	One that is reachable by the heater and whose heat passes most easily to its neighbours, such as a cell near the centre
Temperature sensor	Accuracy within +/- 2 degrees C, sampling interval under 1 s, tip under 1 mm

Values in square brackets are shown that way in the amendment text. Confirm them with your test agency. If runaway does not occur, the pack meets the requirement for that heating method. If runaway occurs, the pack passes when no external fire or explosion is seen by visual inspection without taking the pack apart.

4. Pack design rules (Annex 8K)

Annex 8K lists what the pack maker must build in. The test agency verifies these at type approval and at conformity of production (CoP).

Cell manufacturing date visible on each cell in the format mmyyyy, printed on the pack too. If the date is a code, keep a record of the cell dates.
Cells certified to IS 16893 Part 2 and Part 3 by a NABL-accredited lab or a test agency notified under Rule 126 of the Central Motor Vehicles Rules.
At least 1 charge-discharge cycle of each cell at a C/3 current rate, with the data kept.
A pressure release vent.
At least 4 temperature sensors in the pack. If temperature crosses 60 degrees C, an audio-visual alarm must sound, and if the vehicle is in use the BMS must cut the traction power gradually.
Active paralleling circuits to stop circulating currents between parallel strings, or other circulating-current measures. Fuses or bond wires are the stated alternative.
Enough cell-to-cell spacing for heat transfer and to isolate cells in a thermal runaway, set by cell shape and capacity.
An additional safety fuse or circuit breaker beyond the BMS features.
A traceability document per pack, with cell, BMS and charger details, serial or batch numbers and charge-discharge data.
Cell protection during regenerative braking.
BMS logging of critical pack parameters, with the latest data kept for at least one month, either on the pack or on a remote server.

5. What to prepare

[ ] Get an IS 16893 Part 2 and Part 3 certificate for every cell type you use.
[ ] Draft the risk reduction analysis and the two system diagrams for clause 6.11.
[ ] Log temperature, voltage and the alarm in your test pack's BMS so the data supports the test report.
[ ] Prove the alarm timing: at least 5 minutes before fire or explosion.
[ ] Set up the traceability file for each pack and the one-month data log.
[ ] Ask your test agency which values in square brackets apply to your test.

6. What this page does not cover

I could not open MoRTH's own AIS listing, so I cannot say whether a later amendment changed these clauses. BIS announced IS 18590:2024, a standard for the electric power train of L-category vehicles including the REESS, on 22 June 2024. I did not confirm whether it replaces AIS-156 or applies alongside it. Check the MoRTH and BIS notices before you finalise a design, and take advice from your test agency on type approval.

Questions people ask

When did AIS-156 Amendment 3 apply?

MoRTH notified it on 27 September 2022. Phase 1 applied from 1 December 2022 and Phase 2, which includes the thermal propagation test, from 31 March 2023.

What does the thermal propagation test require?

One cell is heated until it goes into thermal runaway, and the pack must not catch fire or explode. The pack must also give an audio-visual warning at least 5 minutes before any fire or explosion.

How many temperature sensors does the pack need?

At least 4 in the pack, with an alarm above 60 degrees C and a gradual cut of traction power if the vehicle is in use.

Does AIS-156 cover four-wheelers?

No. AIS-156 is for L-category vehicles. The ARAI guide lists AIS-038 Rev 2 as the standard for M and N category vehicles, which have at least four wheels.