12v vs. 2x6v Batteries for Sailboat

[CHM]

I have 4 GC batteries for the house and a regular 12 v for my starter. I have used the Sams Club Duracell FLA batteries in my golf cart and they are excellent and use more when loaded than my boat. I use a 30 amp charger on the boat with no issues.

[Pete7]

Originally Posted by DHHerndon

AGM batteries charge faster, last much longer, and are maintenance free.

The OP said he has a 35A alternator, how will he make use of the faster charging ability of an AGM battery?

Also when you say "will last much longer" compared to what exactly? The forum seems to be suggesting a pair of 6v GC batteries at $160. Seems a good deal to me, wish they were that cheap this side of the pond.



Pete

[FuzzyFeat]

Two 6 Volt deep cycle batteries - the way to go. However make sure you can charge them (or any flooded battery system) FULLY or your batteries will sulfinate, loose capacity and fail prematurely. The alternator alone is not going to cut it.

[Adelie]

Originally Posted by DHHerndon

Your best bet would be to purchase two AGM batteries of the same size that you now have. AGM batteries charge faster, last much longer, and are maintenance free. . . . .

Faster charging only happens if you pony up for a bigger charging system, alternator&regulator and/or shorepower.

Faster charging only results in a savings of 30min or so off of a 7hr charging cycle starting at 50% SoC. If starting at 25% you won’t save any time.

Leaving aside Fireflies AGMs have shorter lives generally from what I read on MaineSail’s site.

The flip side of Maintenance-free is Can’t-Maintain even if you want to.

[Pizzazz]

Interesting how many opinions we have on such a simple topic. For example, a boost converter - sounds great but then how do you charge the 6V battery from your 12V alternator. Then people mention AGM batteries. They are not bad but the main advantages are fast charge/discharge which only makes sense if you run a large battery bank (>600Ahrs) and if you need to install off vertical.

Wet cells are ideal for novices because their tolerance to abuse is the greatest. 60% of the small boats out there run 2x 6V or 4x 6V for house.

[john61ct]

Yes simple is usually best, and in this case the lower cost solution is also better quality.

You never get a full consensus, up to each reader to develop a sense over time of whose opinions to rely on.

If you were paying "an expert" you'd only get one POV.

[Davo1404]

Originally Posted by Pizzazz

Go with the golf cart batteries. You need to accept that they will not be charged fully when underway and that is totally OK, most people use them this way.

One of the advantages of having two 12V batteries is that when one fails down the road, you still have one providing 12V for starting, etc. If one of the golf cart batteries fails, your entire system is down. Most people who use golf cart batteries have 4x, so they can absorb a single battery failure. However, finding good deep cycle 12V batteries at reasonable cost is nearly impossible. Thus, go with golf cart batteries.

If you want redundancy in this setup your cheapest option may be a car starter kit or a small lithium/AGM battery. Your tractor battery is probably shot as well.

I used to have a 12V starting battery and it would always go bad after a few months (undercharging, sometimes used as a house battery, etc.). Then I switched to an AGM 35 AHr battery that I always keep charged via solar. It does start my 18 Hp motor (1000W starter), even if it hesitates sometimes.

Your comment about finding a good 12v deep cycle battery at a reasonable cost isn't quite right. Trojan makes excellent quality deep cycle 12v fla batteries at a very reasonable price.

[john61ct]

J150 or T-1275 being two examples.

Going to be higher cost per Ah than their 6V GCs and the Deka's though.

[PADISail]

You didn't mention the size of the boat, only that it was older...
If you're sailing something over 40-50ft, if I were planning on doing something with limited cells - something less than an 8D x 4 or 6 350A bank, I would go for what has been outlined here, the Maintenance Sealed batteries I would think would be less susceptible to Salt Water Incursion into the cells (even just a high humidity environment could do that), that's why the AGM's and GellCells are popular - Optima Marine's (Blue Top) are a good choice if you decide to go 'spiral gell' and they are not as susceptible to vibration, but don't EVER draw them dead or they are likely to be goners.

Which brings me to the "charging" topic. 35A is not much when you consider it has to power the operation of the engine AND do charging duty.
I've been looking into Hydro Generators as of late, and if you have a few extra bucks to invest you might consider that. Which would pretty much ensure that you wouldn't need to run your noisy generator, and whenever you are underway you would be charging or floating your batts, just to keep them full and ready for use should you need them to keep REQUIRED lighting going IF you happen to get stuck moving on the water after dark... Just a little extra safety margin/backup plan....

I'm guessing you're not interested in solar or wind generator.
And probably the bottom of the line, least $$$, least output of the Hydro would be acceptable, unless you are in a VERY small vessel under 35ft (eg) where it might impact your water drag.

NOTE: I'm not an avid sailor (yet), but I DO know how quickly and unexpectedly electric can be used up and what it takes to generate it...
It's better to have at least DOUBLE the headroom if not TRIPLE the maximum ever needed just to be safe... When designing a residential solar system there is ALWAYS a 3-5 day 'no sun' capacity built in - just in case, and I would think having a reserve is even MORE important when you're days (weeks) away from another soul.

[CaptMDG]

Originally Posted by Cheechako

I have had 3 batteries short out a cell in about 40 years of sailing. So it does happen. You can tell because your bank doesn't hold a charge long. Charge the bank.... Let it sit a bit and feel the batteries. One will be hot to the touch... it's shorted in a cell inside. Strangely, all 3 instances were batteries that weren't more than a year or 1.5 old.
Another interesting thing was, 2 of the 3 were big 8D batteries.

I beat you Cheechako - 3 out of 3 8D's went bad on a single cell! What a waste of money and they were only 2-3 years old. I am going with GC 6 volt batteries from now on.

[rgleason]

Can't resist replying. I'd go with

1. (2) 6vdc golf cart batteries
2. (1) small 50w solar panel if shore power is not available.
3. Make a good big box with room for 4 golf cart batteries (2 future for 430ah bank) back at the alternative location "Diesel" storage near the cutlass bearing & strut, with straps for each battery.
4. Put the 12vdc starter battery in the old location?

I guess I would also get that, boost/buck DC to DC voltage converter that was mentioned.
Wish I had such easy choices!
I would consider replacing that old exhaust hose with a continuous one.
Nice dripless stuffing box.