The best way is direct to the battery with an inline fuse. A main power buss is the next best place. D/F are voltage sensitive, and a low voltage will shut them off. See the post on the fellow that had his Humminbird shutting down. Keep in mind that low voltage and shut downs are hard on the electronics. They ain't cheap so spend a little extra and power them right. IBNFSHN is correct in that they draw very little current, but you still need proper voltage.