Remember, if you want your battery to last a long time, do not allow it to discharge below 50% of its capacity. A voltage of 12 volts is telling you you have reached this point. The depthsounder won't use a lot of power, unless you are driving a monster that reaches deep down, not too useful, normally, for a small sailboat. You will also be using power for the stereo, reading and nav lights, and possibly other things which will pull the voltage down. Your original question made it sound as though the depthsounder is the only use. If so, a digital depth
unit uses much less power than one that displays the bottom (a fishfinder) which needs an electron-hungry display unit. Simple black and white matrix screens, though, use less power than color, high def screens.
I'm sorry, Dudeman, I wasn't carefully reading your original question. I checked the specs for your particular unit, the 365i. It uses virtually no power at all (350 milliamps) for a grey-scale display, depth sounder
transducer and GPS
. That's a great combination at a good price
. You can run that puppy day and night for longer than you will probably be using the boat at any one time.