I added a Lowrance color finder to my bow and TM about a year ago and could not get the wiring thru the bow, past the fuel tank and into the console so I added a 3rd group 24 battery to my anchor well on my flats boat. This added a lot of weight to the bow and all those amp hours were not necessary for such a small draw. It always bothered me but I dealt with it.Recently my home alarm fried and we didn't pay for monitoring anyway since we have 3 dogs which work better. When I was removing it, I noticed that the little backup battery for my alarm was 12 volts so I wired it to my depth finder and it works perfectly, eliminating about 25 pounds from my bow. Since then I found out that's what the kayak anglers use for theirs. It weight about a pound and my smart charger tops it off in about 30 minutes after a day of use.