I finally got the time to add a second pair of batteries to my 42, I had bought a new pair of group 31 AGM’s and a nice Pro nautic 60 amp charger a few years ago and finally found time to install everything. The 2 group 31’s I had been using were technically undersized for starting my Cummins, plus didn’t give me much reserve for when I was off 110v power. On top of that, I’ve always hated where they were located, and those cheap plastic battery boxes suck!
I decided to move the batteries back to their factory locations outboard the engines. Originally the boat came with 2 batteries on the right and one on the left. I was going to replace the boxes with battery holders downs, but Kraig Cupler made a very good point, how much it would suck to crawl over those. So I decided to retain the factory box on the right and make a new dual battery box on the left to replace the single battery box that didn’t survive a shop clean out a few months ago.
For the new battery box, I just made a basic box recreating the Chris Craft box out of some 3/4” marine plywood I had in the shop. I believe it ended up being 15”x18” by 12” tall which gave it the interior dimensions to allow about 1/2”-3/4” around a group 31 battery, and a couple inches vertically. For the cables I cut out slots in the front and back, using a 2” hole saw I put two holes in each end, then used my jig saw to cut out the rest. I then rounded off the edges with my router and some 40 grit before applying 2 coats of Alexseal primer and 2 coats of Alexseal White I had.
For the cables I used 2/0 for the starting circuits, 4awg for the charging cables and 2awg for the charging ground, all Anchor cables. 10’ of black 2/0 gave me enough for the grounds and parallel each battery, and 16’ of red 2/0 got me from the batteries to the previously installed shutoff switches. I decided to mount the battery charger out of the engine room since it’s not waterproof and mounted it in what I call the hellhole, the forward lazerette under my helm. To get there and back I used 37’ of 4awg red cable and 12’ of 2awg black. I used mostly Anchor cable lugs and crimped them with their crimper, which is a very nice unit that gives nice crimps. The exception was connecting to the engine and battery disconnects which required a 1/2” hole and for some reason Anchor no longer make a 2/0 x 1/2” lug, so McMaster Carr to the rescue. I also used heat shrink on all the connections, plus lug protectors on the exposed lugs on the 70 amp breakers I installed in the battery boxes for the charging cables. The charger got hard wired into the existing battery charger circuit using 14ga anchor 3 wire romex, the original wire was hefty, it was tight in a 10/12 connector, they must have had some nutfrier charger originally.
This was a solid 3 day project with lots of crawling in uncomfortable places and as always more expensive than expected, the cables and connectors really add up. I spent about $800 on cables, connectors, shring tube, circuit breakers. The batteries were $250ea and if I remember right the charger was on sale for around $500.
If you have any questions on anything on how I did this, feel free to ask.
