The reason I think the airbag code is related to a dead battery is due to timing. I don't believe multiple things go wrong at the same time.
- alarm started falsing in the cold so I stopped setting it
- battery died a day or two later
- when I recharged the battery, the airbag light was on.
I suppose it's possible the airbag system killed the battery, when I think of it. But I can't see how the system could turn off a power drain. I know that low voltage can cause some weird problems, so I'm going to reset the light and see what happens.
Being able to monitor OBD-II codes real-time is great. We've used that a number of time to diagnose weird problems, especially in modified cars.
