AIS-156 Phase 2 does not require that thermal runaway never happens — it requires that when it does happen, occupants have at least 5 minutes to get out. That is a meaningful engineering target with real design consequences.
- AIS-156 is India's mandatory EV battery safety standard enforced through pre-sale type approval at ARAI, ICAT, or NATRIP.
- Phase 2 (Amendment 4, October 2023) added the 5-minute thermal runaway propagation warning requirement — the most consequential design change in the standard's history.
- Meeting the 5-minute requirement demands co-design of BMS detection speed and physical thermal barrier propagation delay; neither alone is sufficient.
- Amendment 2 mandates cell-source certification, eliminating the counterfeit-cell supply chain that drove the 2022 fire incidents.
- LFP chemistry has a substantially easier path to Phase 2 compliance than NMC 811 due to its 90°C higher onset temperature and absence of cathode oxygen release.
AIS-156 is India's mandatory safety standard for electric vehicle battery packs and systems. It governs what tests a battery must pass before an EV model can be sold, what the BMS must monitor and respond to, and — in its most consequential Phase 2 update — what happens when a cell fails catastrophically. Understanding the standard tells you what Indian EV battery packs are designed to survive, where the design margins are, and why some cheaper EVs in the market represent genuine safety compromises.
Standard Structure and Scope
AIS-156 applies to:
- All electric vehicles classified under L-category (2W, 3W) and M/N-category (4W passenger and commercial)
- Battery packs and BMS units supplied as aftermarket replacements
- Traction batteries (propulsion) — not 12V auxiliary batteries
The standard is based on UN ECE Regulation No. 100 but with India-specific additions for:
- Tropical climate (50°C ambient, 95% relative humidity)
- Road vibration profiles based on Indian road quality surveys
- BMS specifications tailored to observed failure modes in Indian market vehicles
AIS-156 adopts the UN R100 framework but adds India-specific requirements: a 50 °C maximum ambient temperature and 95% relative humidity for tropical climate testing, road vibration profiles derived from Indian road quality surveys, and BMS specifications tailored to failure modes observed in Indian market vehicles. These additions make AIS-156 more demanding for environmental endurance than the European baseline in warm-climate scenarios.
The Test Matrix
| Test Category | Specific Tests | Pass Criteria |
|---|---|---|
| Electrical protection | Overcharge, over-discharge, external short circuit, reverse polarity | No fire, explosion, or electrolyte leakage during/after test |
| Mechanical | Vibration (3-axis road profile), mechanical shock (8g), crush (1000 N/cm² on face) | No fire, explosion, structural breach, >10% capacity loss |
| Environmental | Temperature cycling (-20°C to +60°C, 5 cycles), humidity (95% RH, 7 days), salt spray (48h), IP67 | No fire, explosion, capacity loss >5% post-test |
| Thermal | Overtemperature (external heating to BMS response), thermal runaway (single cell trigger) | Phase 1: No explosion. Phase 2: No passenger hazard within 5 minutes of onset warning |
| BMS functionality | Over-voltage protection, under-voltage, over-current, temperature limits | Correct disconnection within specified response time |
Triggering a single worst-case cell tests the pack's ability to contain propagation — the most dangerous real-world failure mode where one compromised cell cascades through its neighbours. A whole-pack heating test would not expose inter-cell propagation pathways or the BMS's ability to issue a warning before the event becomes catastrophic. The single-cell trigger at the location closest to the passenger compartment represents the worst-case geometry for occupant safety.
The Thermal Runaway Propagation Test (Phase 2)
The Phase 2 thermal runaway test is the most technically demanding and commercially significant change in AIS-156. The procedure:
- The pack is installed in the vehicle or a representative vehicle enclosure
- A single cell (selected as worst-case location — nearest to passenger compartment) is triggered into thermal runaway using a resistive heater or nail penetration
- From the point the BMS warning system alerts (the 'onset'), a stopwatch begins
- Pass criterion: No explosion, fire visible in passenger compartment, or breach of passenger compartment structure within 5 minutes
Engineering implications:
- The BMS must detect thermal runaway onset (generate a warning signal) before the pack becomes a hazard — not after
- Inter-cell thermal barriers must prevent heat from propagating to adjacent cells fast enough to breach the 5-minute window
- Venting paths must direct hot gas away from the passenger compartment
For NMC-chemistry packs, the 5-minute requirement is architecturally demanding — NMC cell-to-cell propagation can occur in <60 seconds without adequate thermal barriers. For LFP packs, the higher onset temperature and lower heat release rate make 5-minute compliance significantly easier to achieve.
The 5-minute requirement is a system-level requirement — it cannot be met by BMS detection alone or thermal barrier alone. A pack where the BMS detects thermal runaway in 10 seconds but the barriers only provide 200 seconds of propagation delay fails the test. A pack with 400 seconds of barrier delay but BMS detection at 350 seconds also fails, because the 5-minute window starts from the warning, not from the onset. Co-design of BMS detection speed and physical propagation delay is essential.
BMS Requirements Under AIS-156
AIS-156 specifies minimum BMS monitoring and protection requirements that apply to all certified vehicles:
| BMS Function | AIS-156 Requirement | Response Time |
|---|---|---|
| Cell over-voltage | Disconnect when any cell exceeds max rated voltage | <2 seconds |
| Cell under-voltage | Disconnect when any cell falls below min rated voltage | <2 seconds |
| Over-current (discharge) | Disconnect at 2C continuous, immediate at >5C | Immediate for 5C+ |
| Over-current (charge) | Disconnect at rated charge current + 20% | <1 second |
| Over-temperature (charging) | Stop charging above defined limit (typically 50°C cell) | <2 seconds |
| Over-temperature (discharging) | Disconnect above limit (typically 60°C cell) | <2 seconds |
| Isolation failure | Alert when <500 Ω/V isolation resistance | <5 seconds alert |
| Thermal runaway warning | Issue warning signal upon detection of TR onset | <2 seconds from detection |
The AIS-156 Amendment History and Why It Matters
L-category vehicles only. Basic electrical safety tests. No thermal runaway propagation requirement. Minimal BMS specifications.
Extended to 4W M/N category. Added IP67 water ingress requirement. Strengthened vibration test profiles.
Added cell-level certification requirement — cells must be from approved/certified sources. BMS firmware must be type-approved with the vehicle.
Clarified BMS response time requirements. Added fault logging requirement (BMS must record fault history in non-volatile memory).
Phase 2 thermal runaway propagation requirement. 5-minute passenger warning requirement. Enhanced BMS thermal monitoring specifications. Effective October 2023 for new type approvals.
Cell Certification: The Supply Chain Requirement
Amendment 2 introduced a requirement that cells used in AIS-156-certified battery packs must be sourced from manufacturers with documented quality systems. This was a direct response to the 2022 incidents where counterfeit or off-spec cells (procured at price rather than quality) were found in failed packs.
In practice, this means:
- Cell supplier must provide material safety data, cell specifications, and quality control documentation
- Cell performance must meet the design specifications used in the type approval submission
- Any change of cell supplier requires re-testing and re-approval
This supply chain requirement has significantly increased compliance costs for small Indian 2W EV OEMs that were sourcing cells from informal channels. It has also improved safety — the incidents involving non-certified cells dropped sharply after Amendment 2 enforcement began.
AIS-156 type approval covers the vehicle model as tested. Pack design changes — different cells, different BMS firmware, different thermal barrier materials — that are not re-approved under the same type approval number constitute non-compliance. Indian OEMs that make unannounced engineering changes to their battery packs without re-testing are both legally non-compliant and creating unvalidated safety systems. Fleet buyers should ask for current type approval numbers and confirm they match the production pack specification.
Request the type approval certificate number and confirm it matches the production battery pack specification — including cell supplier, BMS firmware version, and thermal barrier materials — not just the vehicle model. Ask whether the approval is Phase 1 or Phase 2, since both are in market during the transition period. For newer procurements, insist on Phase 2 (Amendment 4) certification, which requires the 5-minute thermal runaway propagation capability. The ARAI or ICAT online portal allows public lookup of type approval status by certificate number.
Certification Bodies
India has three accredited bodies for AIS-156 testing and type approval:
- ARAI (Automotive Research Association of India): Pune — largest volume of EV type approvals, full test capability including thermal runaway
- ICAT (International Centre for Automotive Technology): Manesar, Haryana — complete AIS-156 test capability
- NATRIP (National Automotive Testing R&D and Innovation Centre): Chennai, Pune, Rae Bareli — newer facilities, growing EV test volume
All three issue CMVR type approvals that are valid for sale across India. Testing timelines for a new model: 6–12 weeks for Phase 2 complete testing, depending on queue.
AIS-156 certification is for the production pack design at the time of testing. It does not guarantee the safety of a specific vehicle after years of field operation, accident damage, or non-approved modifications. Fleet operators should complement type approval verification with periodic pack inspection, BMS fault log reviews, and capacity testing to identify packs that have degraded beyond safe operating limits, regardless of their original certification status.
Key Takeaways
- AIS-156 is India's mandatory EV battery safety standard, enforced through pre-sale type approval at ARAI, ICAT, or NATRIP — no type approval, no legal sale.
- Phase 2 (Amendment 4, effective October 2023) introduced the 5-minute thermal runaway propagation warning requirement — the most demanding and design-consequential change in the standard's history.
- The 5-minute requirement is a system-level target: BMS detection speed and physical thermal barrier propagation delay must be co-designed; neither alone is sufficient, and the 5-minute window starts from the warning signal, not from thermal runaway onset.
- LFP chemistry has a substantially easier path to Phase 2 compliance than NMC 811 due to a ~90 °C higher onset temperature and no cathode oxygen release, but LFP packs still require full AIS-156 type approval testing.
- Cell source certification (Amendment 2) addressed the counterfeit cell supply chain that drove the 2022 fire incidents; fleet buyers should verify current type approval numbers match the specific production pack specification, including cell supplier and BMS firmware version.