Your cranking battery should not be drained or used for long periods of time as this may damage the battery. Having said this, some would be confused that hooking all your accessories to this battery would be the wrong thing to do. Lew mentioned a great point that the electric trolling motor may, and probably will, interfere with your sonar. One of the things I do is set the alarm on my sonar at 10.5 volts, this way I can start the motor and give the battery a quick charge for ten minutes or so. This will not give the battery a complete charge, but enough to run accessories such as sonar, lights, live well, and bilge pump. Love the site and keep up the great work!!