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Old 14-09-2015, 13:39   #16
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Re: Converting Batteries from 8D

I'd only consider 6V golf cart batteries in a wet cell myslef, as I'm unaware of any real deep cycle 12V batteries, and you just can't beat the price per amp. plus being electric vehicle batteries they are built to be heavily used.

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Old 14-09-2015, 13:53   #17
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Re: Converting Batteries from 8D

There's a theme here... And it's wet GC6's are the best overall battery for a sailboat. (Or an RV)

Why 6-volt golf car batteries?
* They're amazingly inexpensive for how much capacity they have.
* They last a very long time if treated well
* If abused (what golf carts do to them) they _still_ last a long time
* Charging is simple/typical FLA stuff.
* They weigh a lot less than 4D's or 8D's.
* You can buy them almost anywhere on the planet. In so cal Costco or Sams for cheapies.

What's the drawbacks?
* You need to check and put water in them every now and then
* Unlike AGM, FLA cannot recharge really really fast. (i.e. most GC6's are happiest being charged at C/10 or lower amperage)

I wouldn't even look at gel. No real advantages for a boat.

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Old 14-09-2015, 14:21   #18
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Re: Converting Batteries from 8D

Last winter I upgraded my system The PO had the house hooked up to the start batteries with an old 50amp charger, which kept boiling the batteries. I considered AGM, but to me they just aren't worth the price and they last about the same as floods if you maintain them properly.

I revamped everything. Go two new 8Ds at about $125 each. I bought a 30 amp, three bank smart charger, electronic smart battery isolator. The only thing that is on the battery charger is the house batteries. I took the start batteries (to include the genny) off the charger. I start my mains and genny at least once a week or I am cruising somewhere.

My house batteries are now 2-banks of 6-6Vdc golf cart batteries from Costco at $83 each.

When on shore power or genny, the charger recharges the house. When I start my mains, the smart Isolator first checks the start batteries and charges if needed, then switches to the house batteries.
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Old 15-09-2015, 05:26   #19
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Re: Converting Batteries from 8D

Originally Posted by dkchen View Post
So I have two 8D batteries that are 5 years old at the moment. They are flooded batteries. I've been wanting to go to AGM batteries, but I think I would have to upgrade my whole charging system to do it. I already had a few big upgrades this year, so I am avoiding that all together.

Looking at finding two 8D batteries on the internet, I find out the literal insane price to ship those things. So I am now thinking of doing two banks of three Group 31 batteries. (I think that is the correct size?) and try to wire them together.

Anything I should be aware of? Will it work the same?

We have three G31s (300 Ah/bank) in place of two 8Ds (~245 Ah/bank). Works fine. Each G31 is much lighter than a single 8D.

Our G31s are Odyssey AGMs; the oldest bank is nearing the end of its 10 season. Shows few signs of deterioration. We are more often at the dock, batteries are easily and often recharged, what Maine Sail sometimes calls "UPS" service. Heavy load when out, even for days or a week or two at a time, but with daily recharging via the genset and then back on the shore charger when we return.

Our old-ish charger manual included directions for charging AGMs. Essentially, use the same settings as for flooded lead-acid. That worked OK with the battery manufacturer's charging recommendations, too.

Not a recommendation, just an observation.

For our oldest bank, when I have to replace, I'm thinking golf cart batteries. Happens I can likely fit 4x GC2s in the same area as our 3x G31s. I'd likely stay with AGMs, but if FLAs could be easily maintained (watered and so forth; access to ours makes that a pain) they'd likely be better bank for the buck.

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Old 15-09-2015, 05:45   #20
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Re: Converting Batteries from 8D

Originally Posted by CarlF View Post

If you do go with more batteries, have the connecting cables made up professionally. I've used Genuine Dealz. You buy the wire, fittings, and shrink tubing from him (excellent quality and prices) , he will make up the cables to your measurements for about $2 an end.

2 AWG Custom Battery Cables Marine Grade by the foot
That guy's cable builder is just too much fun to play with...
In the harsh marine environment, something is always in need of repair...

Mai Tai's fix everything...
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Old 15-09-2015, 06:29   #21
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Re: Converting Batteries from 8D

I don't have one, but there are "systems" that from what I understand make adding water to FLA batteries almost automatic. Seems they are caps that are connected together with a hose and made so that they cannot overfill a battery, so all you do is connect a source of distilled water to this every now and again? No need to open the compartment and mess with each battery?
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Old 15-09-2015, 16:34   #22
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Re: Converting Batteries from 8D

I have two never used, still in box 4D AGM batts $500 for the pair. I'm in MDR.
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Old 16-09-2015, 01:24   #23
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Re: Converting Batteries from 8D

A bunch of guys on my dock all got AGM batteries. One of them has the same boat as myself, and never had an issue when he just forklift the old batteries and put in new AGM batteries. Although, I think he did mention that he put in a new alternator prior to installing the AGM batteries.

I am going to the boat next week to take a look at the alternator to see if it can push out well.

Have you guys heard of this website? Scorpion 12v 250AH Deep Cycle 8D AGM Battery SP250-12

The shipping is amazing to the point that I am questioning it.

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