I bought a portable depth finder for my boat (LCR400ID) that runs off 2 6-volt batteries. (lantern batteries) Can I just snip that cord and splice in an extension and run to one of my 12 volt boat batteries for power? Seems the voltage wold be the same... Please advise- Stan

It would work only if the two 6-volt lantern batteries are wired in series (the positive of one is connected to the negative of the other). If they are wired in parallel (pos to pios and negative to neg) then the device is running on 6 volts, not 12, and you can't do as you suggest. The advantage of using two batteries in parallel like this is that it provides higher current capability and/or longer battery life.

If you find that indeed the two 6-volt batteries are in series then your proposal should work, but be very careful to get the polarity right.

Since this is portable, you could use a cigarette lighter plug.

Thanks guys..! Will check specs on unit to make sure it is a 12 volt unit since the wiring is not exposed in the "portable case". I like the lighter idea and I could always use that for other things... just did not want to melt down while on the water and have to jump in due to fire since the water is still very cold in Kentucky... My sincere thanks