How Adhesives, Sealants & Potting Compounds Help EV Batteries Meet India’s AIS-156 Safety Standards
Reading Time: 5 minutesAIS-156 EV battery safety is now a design requirement, not an afterthought. Every EV battery pack sold in India has to pass AIS-156 before it reaches the road — and increasingly, whether it passes comes down to the bonding materials inside it, not just the cell chemistry or the battery management system. Potting compounds contain heat when a module starts to fail. Sealants keep water out to an IPX7 standard through monsoon after monsoon. Structural adhesives keep cells and trays from shifting under years of vibration. For pack designers and Tier 1 manufacturers working toward AIS-156 EV battery safety, this is where each of those materials fits, and what AIS-156 actually asks a pack to survive.
AIS-156 EV Battery Safety: What must an EV battery pack pass to be sold in India?
AIS-156 is the Automotive Industry Standard governing traction battery safety for L-category vehicles — two-wheelers, three-wheelers, and quadricycles — while a parallel standard, AIS-038 (Revision 2), covers M and N category vehicles: passenger cars and larger commercial EVs. Both take a system-level approach, treating the battery pack and its supporting electronics as one unit rather than certifying cells in isolation.
The current requirements were rolled out in two phases: Phase 1 from December 2022, and Phase 2 from March 2023, which added tests like EMC validation of the battery management system, mandatory audio-visual warnings ahead of a thermal event, and active parallel circuits that can isolate a faulty string of cells. The Bureau of Indian Standards has continued building on this foundation, publishing IS 18590:2024 and IS 18606:2024 to further formalize powertrain safety and performance requirements across vehicle categories. For manufacturers, none of this is optional paperwork — it’s a homologation gate, and a pack that fails late in development is a launch-timeline problem, not just an engineering one.
Two tests inside this framework matter most for how a pack is physically built: a water-ingress test and a thermal propagation test. Everything below traces back to one or both.
What is thermal propagation, and how do potting compounds help contain it?
A lithium-ion cell can fail internally — from a manufacturing defect, physical damage, or an electrical fault — and enter thermal runaway, releasing heat rapidly. On its own, a single cell failure is a contained, manageable event. The real risk is propagation: that heat transferring into neighboring cells and modules until one failure becomes a pack-wide fire. AIS-156’s thermal propagation test exists specifically to confirm a pack can absorb and contain that heat rather than pass it along.
This is where potting compounds do structural work, not just cosmetic work. A potting agent fills the space around a module, and that fill does two jobs at once: it adds physical mass and distance between failure points, and — in thermally conductive formulations — it actively pulls heat away from a hot spot toward the enclosure or a heat sink, rather than letting it radiate sideways into the next module. ThreeBond’s TB2045B and TB2145B lines were developed specifically for this kind of heat dissipation in EV components, and the same chemistry that manages routine operating heat during charging and discharge is what buys a pack precious extra seconds during a genuine thermal event.
What IP rating does a battery enclosure need — and how do sealants get it there?
Under AIS-156, a battery pack at full charge has to withstand an IPX7 water-immersion test — roughly a metre of water for half an hour — without a fire, an explosion, or a loss of function. That’s not a theoretical bar in India: battery packs on two- and three-wheelers sit low to the ground, and monsoon flooding puts them in standing water routinely, not occasionally.
Getting to IPX7 is a sealing problem at several points at once: the main enclosure seam and lid, every connector and harness entry point, and the battery management system’s own housing. Silicone sealants are the default choice in general automotive sealing, but inside a battery enclosure, silicone’s tendency to outgas and migrate can interfere with nearby electrical contacts and sensors — which is why non-silicone sealant chemistries are increasingly specified for this application specifically. For the main enclosure seam, form-in-place gasketing (FIPG) is often the more practical choice over a cut gasket, since it applies precisely on a moving assembly line and cures into a seal with no joint of its own to fail.
Where exactly do adhesives, sealants, and potting agents sit inside a battery pack?
Put together, a compliant pack is really relying on several separate jobs, done by different material families working alongside the cell chemistry and BMS:
| Battery pack location | Failure risk it addresses | Related AIS-156 requirement | ThreeBond product category |
| Cell-to-module and module-to-tray bonding | Shifting or fatigue under vibration and shock | Mechanical/vibration durability | Structural adhesives |
| Module potting | Heat transfer between cells during thermal runaway | Thermal propagation test | Potting agents/epoxy (thermally conductive grades) |
| Enclosure seam and lid sealing | Water and dust ingress | IPX7 water-immersion test | Sealants, form-in-place gaskets (FIPG) |
| Connector and harness entry points | Short-circuit from moisture ingress | IPX7 water-immersion test | Sealants (non-silicone) |
| Enclosure fasteners | Loosening over the vehicle’s service life | General durability | Threadlocking agents |
Structural bonding carries its own complication worth flagging: battery trays are frequently aluminium for weight, paired with a steel or composite enclosure for protection — a dissimilar-metal joint that welding handles poorly, but that a structural adhesive is well suited for.
FAQ
Is IPX7 legally required for EV batteries in India?
Yes. Under AIS-156 (and AIS-038 Rev 2 for larger vehicles), a battery pack at 100% state of charge must pass IPX7 water-ingress testing with no fire or explosion during or after the test.
What actually stops one cell fire from becoming a full pack fire?
The thermal propagation test is what certifies this, and packs meet it through a combination of physical cell/module spacing, thermal barriers, and the heat-dissipating or insulating properties of the potting compound surrounding each module.
Do adhesives and sealants really affect crash and fire safety, or is this just assembly convenience?
They affect it directly. Structural adhesives keep cells in their designed position during an impact instead of letting them shift and short against each other; sealants and potting keep the enclosure from flexing open or admitting water during exactly the kind of event AIS-156 is testing for.
AIS-156 compliance is easiest to design in early, not test for late. ThreeBond India’s technical team works with EV and battery pack manufacturers from the design stage to match potting, sealing, and bonding materials to the specific tests a pack needs to pass. [Contact us / Explore our Automotive Market solutions] to talk through your battery pack’s requirements.
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