Boeing 737 - Dead battery implications.
Just doing a bit of revision regarding the 737.
If on the IRS panel both "DC FAIL" lights were to illuminate it would indicate a dead battery (we're talking inflight, not at alignment). So no back up available if the generators are both lost.
However someone pointed out that a dead battery also limits your fire protection. Assuming you had both generators online, but the "DC FAIL" lights on the IRS panel came on it would indicate a dead battery. Detection for Fire is powered off the battery bus which would still be powered but the extinguishers are powered off the hot battery bus which would no longer be powered. So you would see you had a fire but you'd be unable to put it out!
have I got this right? Dangerous to ask on a anonymous forum but all thoughts welcome!