Dual battery setup.  The red top takes care of only starting the motor.  The yellow top does everything else...stereo, radios, winch, etc.  They are charged by the same alternator (which also runs the welder) via an isolator.  I can run the red top all the way down, and still start the motor, no problem.  The setup also insures that the starting battery always has adequate voltage to run the motor's PCM.