[asphaltgambler]

My understanding, as some have touched on above, is when an impact is severe enough that airbags deploy, the battery current is disabled. BMW does this by 'shorting' a fusible link in the main power accessory feed by the body control module. It is not serviceable, you have to replace the whole line. i suspect other manufacturers have followed suit. The purpose is to avoid fire or other hazard by shutting down the electrical system.