Seeking Battery Advice

[Jim in TC]

We will pick up our 2006 Sun Cat next week. The batteries (2 AGM batteries are original, part of the full electrical package for this boat) are dead as a hammer. I am looking at replacement. Since we will mostly daysail from a slip that has shore power, our onboard electric needs should be modest. At the same time, the onboard batteries will be the 'backup power' via a 12v charging plug for the Torqeedo motor.

In trying to maximize value while reducing overall cost, I am finding only a few options. One would be to get one really high quality true deep cycle battery (like the Optima, seemingly well liked but pricey). Another option, at higher cost, is to replace both with new 'conventional' AGM but I am finding few options that are not 'dual purpose' (starting and deep cycle combined). An option I have not been able to find is a flooded lead acid sealed deep cycle battery (lower quality than AGM but probably good enough, if I could find it). Lots of those that are not sealed...

What are you using on your boat and brand or where-to-purchase advice would be helpful. What has worked for you (and not)? Would you consider dual purpose batteries?

Thanks!

[wes]

Strongly recommend true deep-cycle batteries, either conventional flooded or AGM. After massive research I settled on Lifeline or Trojan AGM. If you want a good quick education in batteries for sailboat use, here's an excellent starting point:

https://marinehowto.com/what-is-a-deep-cycle-battery/

Wes

[Jim in TC]

Helpful and comprehensive information! It all makes sense to me, too, as we lived 'off the grid' with batteries for many years before this. But the marine battery system is confusing...and apparently rife with false or misleading claims. I am looking toward smallish but true deep cycle golf cart or wheelchair batteries now.

[Potcake boy]

Jim,

Installed a Mastervolt group 24 AGM in my Suncat. Had a 20 watt solar panel mounted just behind the mast. The power was used mainly for the GPS, but also served to power cabin lights occasionally. The battery stayed pretty much fully charged. I have used Mastervolt AGM batteries for a good few years and have had excellent service, including a group 31 house battery in  my present boat.

[DanM]

Struggling with the same issues. Has anyone replaced the "festoon" bulbs in the running, masthead, and anchor lights with LED's? I experimented  with a portable jumpstarter as some have suggested, but the power ran out in an hour or so. So I'm wondering if, by reducing demand to a tenth of the draw of regular bulbs by installing LED's, I might get by for the couple of times a season that I may want running lights for a couple of hours. Just trying to avoid getting involved again with the whole battery/solar charger thing which I find baffling and overkill for my daysailing usage.

[DanM]

PS-I am also considering just buying portable, clamp-on, battery-powered LED Nav lights. We've already put stick-on LED puck lights (incredibly cheap but effective hardware store item) in the cabin and they work great. I've tried for an easy solution to the boat-power problem just because it goes against my grain to have the factory-installed electrical system sitting on the boat but not functional-  I just got stubborn about it but truth be told, the portable lights are probably the rational choice for our application,  and less cost and effort than a real marine battery set-up.

[Jim in TC]

So replacing bulbs with LEDs makes great sense to me...and I intend to do at least some of the bulbs once I get the boat. They are pricey but should last pretty much forever, and as you say will draw a fraction of the power. Batteries Plus has them (probably cheaper than West Marine) and maybe less costly yet on Amazon.

Meanwhile, I am considering a smaller but quality deep cycle battery system (I, too, resist the idea of a built in electrical system and not making use of it). https://www.batteriesplus.com/productdetails/sladc12=35j  These 35 AH batteries from Batteries Plus suggest the possibility of 150-250 cycles at 100% discharge (that higher number, at 100%, seems a bit optimistic, but still...) at a cost well under $100 (after discounts) per battery. My reading suggests that a lot of the marine batteries, even those advertised as deep cycle, are not particularly, um, deep. These Duracell Ultras are used mostly in wheelchairs, made to cycle, are small and light (relatively), sealed and keep my investment low enough that I might use the savings to add a small solar panel and charge controller to the system. These do not have a 'core charge' and can even be shipped relatively easily, if necessary.

[Tom L.]

All good ideas but here is one you may not have thought of. My Sun cat had a big battery up along side the mast. Very heavy and a Royal pain to take out  or service.

I scaraped that monster and replaced it with a jump starter. Yep a plain old Harbor Freight $35 jump start battery. Works perfect for the very minimal requirements for the boat.

My largest draw was a sounder that is very desirable for the shallow waters of Florida. I usually only spent two consecutive nights aboard and it was great for that. The beauty is when I leave the boat I simply take it with me, which is lighter than my tool box, and plug it in back home to recharge. It can also be plugged in at a marina if you use marinas. We usually anchored out at night.

We had a couple of dry cell battery powered fans with a few extra cells too cool down when required. I have a Garmin 78SC gps/plotter also with AA batteries. Finally I had a couple of bump lights again with AA cells. All dry cells are AA so I carry a bunch of spares and toss the old ones.

So the long and short I never really depleted the Jump Starter.  And you will have a jump starter for the tow vehicle when you return and find an inside light had been left on.

A simple no frills/ economical solution for a boat that is so small.

If you add an auto pilot this may not be enough power.