Quote Originally Posted by Barnacle Bill View Post
Its due to voltage drop caused by the size and length of the wire. Electronics like a depth finder draw very little amperage so small wire is commonly used. You are OK at 11 volts.
Small wire was adequate for the electronics of yesteryear, but today's units with large color displays plus GPS, SI, DI, etc. consume more amps. When I replaced a HB 575 with a HB 1197, the extent of the consumption increase surprised me. At the time, the 575 was on a stand-alone 7.5 Ah 12v battery. One fully-charged battery lasted for a full 12hr+ fishing day. The 1197 killed one of these batteries in less than 2 hr. My quick fix was a pair of wires salvaged from the latest trailer re-wiring project. These wires ran the full length of my 16' boat from the 1197 up front to the starter battery. This was a long run and the wire size was small, so instead of one pair, I used two. Even then, the 1197 reported voltage that occasionally fell below its automatic shutdown point--10 volts. I'm now using 12 ga wire and only seeing a drop of about .5 volts.