That and the fact that the elt battery has a current limiting fuse in each leg and is in
a sealed enclosure.
Syseng68k, You're right. But, I think, even without fuses, the battery leads, if shorted together or to ground, would probably just melt through, stopping the current flow, before the battery barely got warm to the touch, and in a sealed environment, there wouldn't be enough oxygen to sustain a fire long enough (if one even started inside the ELT), that would burn through the enclosure.