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Old 03-31-2015, 07:23 AM   #41
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Thanks again guys. As recommended, I'm going to focus my charging efforts on the two AGMs at 10.5 volts and most likely take the other two to a battery shop for a proper diagnosis.

When I think all this probably could have been avoided . . . My head's really sore from banging it against the wall.


Battery shops sell batts , to discover the state of a charged or discharged batt takes a special meter.

The local golf course golf cart guy , or the folks that sell and service golf carts will have the proper meter to actually test a batt.
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Old 04-05-2015, 06:22 PM   #42
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Winterising your Boat.

Wow, we in Oz have boating far too easy, I feel for you guys in the far north. Down here we can boat all year around and it is only the cyclones which appear between November and April here in Qld. which would cause us to head south instead of north for that period.

Boating all year around, we just don`t know how lucky we are.

I do feel your pain guys.

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Old 04-06-2015, 10:01 AM   #43
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Update on My Little Drama

After sifting the advice from this group and talking to some battery manufacturers, I decided I needed a better charger, so I got one of these.



Great little unit that works for gels and AGMs with desulfation and restoration modes. I showed it to the marina owner and he was OK letting me leave it hooked up overnight (these are supposedly used for months at a time by car guys).

After 40+ hours, the first battery was at 12.72 volts this morning. I will check this evening to see if it's holding. Currently, charging the second 8A8D.

I've also been talking to a local Deka dealer who can get me 4 of these quickly if the worst happens and the batteries fail to hold a charge.

BTW, I learned they are 4.5 years old.

Will post how this all turns out.
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Old 04-06-2015, 09:34 PM   #44
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Time for New Batteries

Well, after getting my hopes up, the first battery did not hold it's charge and the second one would not accept a charge whatsoever. So, now the question is whether to replace with AGMs or lead acid.

Any opinions?
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Old 04-06-2015, 10:02 PM   #45
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Well, if you're replacing 2 8D batteries and you have an extra inch or so of headroom, you can fit 6 golf cart batteries in the same space. If you have good access and don't mind servicing the bank, lead acids are damn good bang for the buck. If money's no object, AGM is the way to go.

Make sure your charger is up to the task of the battery bank type and AH size, whichever route you decide to take. Adding a state of charge battery monitor will help you keep track of all those amps coming and going.
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Old 04-06-2015, 10:08 PM   #46
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AGM all the way for this lazy lad.
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Old 04-06-2015, 10:40 PM   #47
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How many batteries and banks do you have now? Do you have to replace all or just some? If you are keeping some of the batteries, what kind are they?
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Old 04-07-2015, 12:01 AM   #48
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How many batteries and banks do you have now? Do you have to replace all or just some? If you are keeping some of the batteries, what kind are they?
Not counting the gen set, I have two banks, each of which has two Deka Intimidator 8D AGMs. I have to replace all 4, which I can do for $495/ ea.

There's one bank outboard of each main engine, not ideal for heat or access. Golf cart batteries sound appealing for price and weight (compared to the 8D beasts) but I'd need taller boxes and cables. 8D AGMs would be an easy plug and play (except for the weight).

Edit: I need to measure the battery boxes. There just may be another inch of headroom.

These AGMs are 4.5 years old. The cases are bulging on all 4 of them, which I guess means they were overcharged at some point, so I don't know how much more life was in them. (They were that way in the survey photos last year.). There is no sign of cracked cases or leaks.

The boat has a Xantrex Truecharge2 40 amp charger. I'll probably add an inverter/charger this year. I'm hoping this charger isn't responsible for any overcharging that may have occurred before we bought the boat.

The AGMs are also appealing for relative lack of maintenance, no spills and low discharge over winter (if you don't lave them connected to parasitic loads like I did). Is there any real performance/longevity advantage in the golf cart batteries vs these AGMs (which are rated at 245 ah each) or is the difference primarily weight and price?

Thanks.
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Old 04-07-2015, 01:47 AM   #49
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Is there any real performance/longevity advantage in the golf cart batteries vs these AGMs (which are rated at 245 ah each) or is the difference primarily weight and price?


With the LA GCs, you get ~50% greater capacity. That's a huge performance benefit if you can service and charge appropriately.
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Old 04-07-2015, 02:28 AM   #50
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4.5 years for AGMs doesn`t sound great, I get that out of cheaper unsealed L/As which are less fussy about charging. You might have a charging issue, considered the alternators as well as the charger?
Though Oz is famed for high prices, I see 200Ah + 8D AGMs for around $400 on Ebay, even some 260Ah ones. I`m shopping for an 8D L/A.
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Old 04-07-2015, 06:52 AM   #51
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The AGMs are also appealing for relative lack of maintenance, no spills and low discharge over winter (if you don't lave them connected to parasitic loads like I did). Is there any real performance/longevity advantage in the golf cart batteries vs these AGMs (which are rated at 245 ah each) or is the difference primarily weight and price?

From reading, 6v golf cart batteries are said to be true deep cycle batteries, whereas 8Ds are almost always said to be really dual-purpose -- even if the label says "deep cycle." Different design in the GCs, thicker plates, better for deep cycling.

Pairs of 6v GCs at 12v usually give you about 220 Ah/pair. If four will fit where one of your current 8Ds fits, it'd be ~440 Ah vs. ~245 Ah. Or if six will fit where a pair of your current 8Ds fit, that be ~660 Ah vs. ~490.

No spills is an AGM (and gel) feature, as is reduced (not eliminated) off-gassing. Low self-discharge rate is also a feature that I've confirmed with our AGMs over winter. No maintenance is a good thing. OTOH, a flooded lead acid (FLA) system with a battery hydration system installed may be way less expensive.

To compare costs, you'd ideally look at cycle life specs (as in cycles to 50% depth of discharge/DoD), and work out cost/Ah for the whole (predicted) life of a given bank. From reading, FLA GCs (e.g., Trojan T-105s) give you about the best bang for the buck (unless you buy brand X from Costco).... but I still prefer the AGMs. (And BTW, Lifeline makes 6v AGMs; maybe others do, too.)

There are "premium" AGMs (Odyssey, Lifeline, etc. -- and Sears Platinum G31s are made by Odyssey) and then there are the others (Deka and so forth). The former often say stuff about "pure lead" (not recycled) in their products. Dunno whether you can use their marketing words to compare. Probably still safer to compare using cost/Ah over the predicted life of the battery.

Our oldest bank of 3x Odyssey G31 AGMs is now entering it's 10th season.

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Old 04-07-2015, 10:53 AM   #52
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Do you have three start banks and no house bank? I believe you said earlier that your genset has its own 8D battery? It sounds like what you have is essentially 3 start banks and no house bank. If so, you should probably get batteries that are dual purpose (starting and deep cycle). I'm sure that the 6V batteries will start your motors. I don't know if they are really designed for starting loads. Maybe someone else has used the 6V in a starting application and can add their experience. I have 2 4D batteries in my house bank, and will probably replace them with a 6V setup when the time comes.

If the batteries are easy to get to and you are inclined to regularly water them, quality flooded batteries, 6V or 12V will give you long service.

Personally I like AGM batteries. Low maintenance is a nice feature. I have too many shirts and pants with holes in them caused by my poor battery checking techniques.

A Xantrex Truecharge 40 came with my boat. I found that it was overcharging the batteries. I got rid of it and installed a Victron Phoenix charger. If you suspect overcharging, you should fix that problem before you put new batteries in the boat. No sense in damaging your new batteries with a bad charger. Check the voltage at the battery with a voltmeter, don't rely on the electrical panel meter. If your charging system checks out OK, I guess the bulging could have been caused by freezing.

Those 8D batteries weigh around 160 lbs each. Good luck getting them out and the new ones in.
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Old 04-08-2015, 06:53 AM   #53
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Do you have three start banks and no house bank? I believe you said earlier that your genset has its own 8D battery? It sounds like what you have is essentially 3 start banks and no house bank.
Thanks for your thoughts. We do have 3 banks, two of which serve both house and main engine starting purposes. I'm far from knowledgeable about 12-volt systems, but have read and been told that doing double duty is not an unusual set up with large AGMs.

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A Xantrex Truecharge 40 came with my boat. I found that it was overcharging the batteries. I got rid of it and installed a Victron Phoenix charger. If you suspect overcharging, you should fix that problem before you put new batteries in the boat. No sense in damaging your new batteries with a bad charger.
Exactly my concern. I'm going to have the Xantrex checked first. If it's OK, I'll probably keep it as a backup and install an inverter/charger.

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Those 8D batteries weigh around 160 lbs each. Good luck getting them out and the new ones in.
Oh, yeah! They are beasts. Weight, price and location (tucked outboard of the main engines) are the only things I don't like about AGMs on my boat; otherwise they'd be a great choice.

I'm going to do some more research and decide whether to stay with them or totally redesign my battery banks. For instance an 8D that only starts the genset seems like overkill. L16 golf cart batteries sound appealing for a house bank. True deep discharge, smaller footprint for the same amp hours, 60% of the 8Ds' weight and lower price vs more battery maintenance and new, taller battery boxes. But I still have a lot of thinking to do.

My immediate concern is getting two engines running on one good AGM to be able to move the boat 30 miles or so to where I'm going to have some work done. My tentative plan is to move the remaining good generator AGM into one of the main engine starting bank boxes and hook only that battery up. (With 1440 cold cranking amps, it should be able to crank both Lehman 135s.) I'm told that if I disconnect, cap off and tape up the leads on the opposite battery bank and set the battery switch to "both," I should be able to start both engines and run the boat safely for this day trip.
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Old 04-08-2015, 07:17 AM   #54
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L16 golf cart batteries sound appealing for a house bank. True deep discharge, smaller footprint for the same amp hours, 60% of the 8Ds' weight and lower price vs more battery maintenance and new, taller battery boxes. But I still have a lot of thinking to do.

Lifeline makes L16 AGMs.

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Old 04-08-2015, 10:20 AM   #55
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If you completely disconnect a bank from the motor you will not be able to start it. Your starter is connected to those batteries. You will need to connect the starter cables to the good battery.

Since you will eventually need a new (smaller) battery for the genset It may be easier to get that battery now and use it for the second engine. I would think that a group 27 or 31 would be sufficient to start your motor. After you decide on a new battery setup, move that battery back to the genset.
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Old 04-08-2015, 01:30 PM   #56
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My tentative plan is to move the remaining good generator AGM into one of the main engine starting bank boxes and hook only that battery up. (With 1440 cold cranking amps, it should be able to crank both Lehman 135s.) I'm told that if I disconnect, cap off and tape up the leads on the opposite battery bank and set the battery switch to "both," I should be able to start both engines and run the boat safely for this day trip.
Sounds like this should work. Of course, your unused leads will be hot, but you know to insulate and secure them well. If a twin engine, will both alternator hots be connected? You don't want to blow a diode or cause a problem with running an alternator when disconnected.
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Old 04-08-2015, 02:31 PM   #57
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Al, do you mean connect both alternator hots to the same battery?

I'm now leaning toward Blue Yonder's suggestion of getting a Group 31 that I can use with the genset going forward. That way, I'll have one batt on each bank.
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Old 04-08-2015, 02:44 PM   #58
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I'm no alternator expert, but I've been told not to run an alternator that is not connected to a battery to avoid causing damage. I think your plan to purchase a G31 for later use is a good one so both starters are connected to a battery while you're repositioning.

Don't know how your boat is cabled, but many run the alternator charge back through the starter cable to provide the battery charge. In some cases, there's a wire running from the alternator to the starter lug to make the connection. Mine was like that until I recabled and ran a larger cable from the alternator directly to the hot battery buss.
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Old 04-08-2015, 03:04 PM   #59
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Thanks for raising that. I'm not sure how the boat is cabled either, but I'll get somebody to check it out. Hopefully, using a second battery will make all this moot.
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Old 04-10-2015, 11:16 AM   #60
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About to buy a Group 31 for the starboard bank. I'll move the remaining good 8D AGM to the port bank. Connecting only these two batteries, I'm told, will give me enough to start both engines and run certain DC loads (like bilge pumps).

This is a short term fix to allow me to move the boat next week and ponder how or if I want to redesign my DC system.

A battery shop tells me that my Xantrex Truecharge2 charger should be able to deal with these dissimilar battery types simultaneously while the boat's on shore power (maybe a week or so). He suggested using the AGM setting.

Anyone have any thoughts on this?

Also, if anyone's using Group 31s to start FL SP135s, I'd love to know the cold cranking amps you're needing.

Thanks!
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