Literally, the first thing we do when we start any new battery development is a test for a thermal runaway scenario. Thermal runaway is when there’s an uncontrollable increase in temperatures, which can cause fires. Thermal runaways can occur due to a variety of reasons but the primary ones are short circuits, cell internal short, and mechanical abuse. The BMS and other short circuit protection in the battery protect the pack from any shorts. There are actually three levels of short circuit protection.
On the mechanical abuse side, we’ve placed the pack in a place where it is shielded from external abuse as much as possible. We’ve had 450’s crash and the battery comes out unscathed in pretty much every case. This is also a reason why we prefer an aluminum casing. It also helps keep the battery cool. The cell spacing and thermal management inside the pack are also designed in a way so as to ensure that in the event of a thermal runaway, the fire doesn’t spread from one cell to the other.
All that said, cell internal shorts can still occur because of manufacturing issues at the cell supplier’s end. This is the reason we only source cells from Tier 1 suppliers, even if this comes at an extra cost. Ather currently has in excess of a million cells on the field. To ensure we are absolutely sure that the rider will be safe in a one in a million event, we conduct tests over and above regulatory requirements to simulate a thermal runaway due to a cell internal short circuit event. Only after we pass these tests do we clear the battery pack design for production.