[Milsurplus] Running mobile on lead-acid batteries

[Hue Miller]

Let's imagine a liaison transmitter, BC-375 or ART-13, running off 
a car battery. A good sized car battery seems to have about 150 AH.
I am wondering how long this radio would run key-down from the
battery. This drain i am thinking about is about 50-60 amps. Of course,
the radio will not run down to zero volts; i think it would maybe cut out
around somewhere in 7-9 volts. While the input power to the final 
would tend to go down as the square of the ratio to full high B+, when
the heater voltage is varied downward at the same time, the input
power will fall off even more rapidly. Anyone have experience with
such a operating situation, or does a military manual you know of,
address such situation? Appreciate any input!  Tnx-  Hue Miller