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Old 09-08-2022, 13:51   #1
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Assistance with Battery choice

Hello Everyone,

For the past several weeks I've been dealing with a battery capacity lesson and am seeking feedback from anyone that may have had experience with Deka Batteries.

First off I currently have 2 group 31 12v, 100AH West Marine flooded batteries that I already replaced once. Since the boat is new to me I'm having to go through that Power Management learning curve. A few weeks ago when I visited the boat on its mooring I left the refrigerator on. When I returned all batteries were drained including my third battery, the starting battery. Since I had upgraded my Solar just recently to 2 200W panels I have wanted to size a suitable Battery Bank including future growth needs. I felt that two flooded batteries were probably not going to cut it, considered going to Lithium but simply cant afford them right now. After much research on the different types I'm pretty much set on purchasing 4 AGM batteries which are also not inexpensive. At present I've zeroed in on some Deka batteries and am hoping some of you can let me know what your experience has been with them. They are the Deka 8a31dt-deka model which is a 12v, 105AH battery. See spec sheet attached.

Has anyone used this battery and what was your experience overall??

Thanks in advance.
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File Type: pdf Deka GP 31 AGM.pdf (559.5 KB, 31 views)
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Old 09-08-2022, 15:05   #2
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Re: Assistance with Battery choice

Your problem is not battery capacity, it's charging capacity. If your current setup can't handle a fridge alone then you are seriously under-charging. Also your start battery should be separate from the house bank as you have found out,. You could add a VSR (voltage sensing relay) from the house to the start battery to keep it topped up. As for battery chemistry, I would avoid AGM's due to their cost and maintenance requirements and stick with good all lead acid or DIY lithium for much less than the AGM's.

I haven't used the Deka AGM's but their calcium batteries are quite good.
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Old 09-08-2022, 15:23   #3
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Re: Assistance with Battery choice

Quote:
Originally Posted by Cap Morgan View Post
Hello Everyone,

For the past several weeks I've been dealing with a battery capacity lesson and am seeking feedback from anyone that may have had experience with Deka Batteries.

First off I currently have 2 group 31 12v, 100AH West Marine flooded batteries that I already replaced once. Since the boat is new to me I'm having to go through that Power Management learning curve. A few weeks ago when I visited the boat on its mooring I left the refrigerator on. When I returned all batteries were drained including my third battery, the starting battery. Since I had upgraded my Solar just recently to 2 200W panels I have wanted to size a suitable Battery Bank including future growth needs. I felt that two flooded batteries were probably not going to cut it, considered going to Lithium but simply cant afford them right now. After much research on the different types I'm pretty much set on purchasing 4 AGM batteries which are also not inexpensive. At present I've zeroed in on some Deka batteries and am hoping some of you can let me know what your experience has been with them. They are the Deka 8a31dt-deka model which is a 12v, 105AH battery. See spec sheet attached.

Has anyone used this battery and what was your experience overall??

Thanks in advance.

some thing is off here . do not buy those AGMs

I have a fridge on teh Bav , in upto 39 degrees C ambient , I have 280 AH wet acid ( 2 x 140aH batteries ) and 2 x 200W solar ( with Victron mppt)

my fridge averages 25-30 ah during night hours , my solar easily keeps up during the day and at night i suffer about 10% SOC loss

something is wrong , in your setup , and your starter definitely should not be flatten by the fridge

dont buy AGMs anyway , not a good battery for a boat , get reasonable quality sealed Wet acid
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Old 10-08-2022, 03:18   #4
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Re: Assistance with Battery choice

If you have the room - and it sounds like you do - I would go with a bank of 4 golf cart batteries. You wire them in two sets of series and then those two together in parallel. But you can get these very cheaply and they are tough and last many years.
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Old 10-08-2022, 04:27   #5
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Re: Assistance with Battery choice

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Originally Posted by Cap Morgan View Post
Since I had upgraded my Solar just recently to 2 200W panels I have wanted to size a suitable Battery Bank including future growth needs. I felt that two flooded batteries were probably not going to cut it, considered going to Lithium but simply cant afford them right now. After much research on the different types I'm pretty much set on purchasing 4 AGM batteries which are also not inexpensive. At present I've zeroed in on some Deka batteries and am hoping some of you can let me know what your experience has been with them. They are the Deka 8a31dt-deka model which is a 12v, 105AH battery.

Sounds to me like your solar and/or charging systems aren't working as expected.

I dunno Deka AGMs. Have had good luck with both Odyssey G31s and Lifeline 6Vs (both of which are even more expensive, but we got 11-12 seasons out of them...).

If you look up the Compass Marine site, I think Rod Collins (posts as Mainesail, here) has offered some commentary about Odyssey/Lifeline vs. all other AGMs.

-Chris
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Old 10-08-2022, 04:56   #6
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Re: Assistance with Battery choice

The most cost effective solution would be going with 6v golf cart batteries as was suggested. Two would give you similar AH capacity to what you currently have while 4 would double it. Sounds like the dead battery incident occurred before you put on the 200 watts of solar. That should be plenty to keep up with the refrigeration. And as has been suggested, figure out why the start/reserve battery was dead and consider something like an ACR to minimize the chance of that happening again.
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Old 10-08-2022, 05:27   #7
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Re: Assistance with Battery choice

Another vote for 6v golf cart batteries instead of AGMs. Best bang for the buck, downside is you will need to add distilled water every 2 months to top off the cells. Not a big deal.

Also agree with another comment something is wrong with your setup. Your 400W of solar should provide plenty of power to keep the fridge running. Do you know how much power your fridge draws? If it's drawing more than the specs, would check your box insulation. Would add more insulation, especially if it is original on your Cal.
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Old 10-08-2022, 10:56   #8
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Re: Assistance with Battery choice

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Another vote for 6v golf cart batteries instead of AGMs.

Just a comment that these are not mutually exclusive; 6V AGMs exist.

We used the latter for one bank because access for watering was non-existent in that location.

Not a recommendation, just an observation.

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Old 10-08-2022, 12:32   #9
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Re: Assistance with Battery choice

Lifeline makes excellent 6vdc AGM batteries, and they are excellent! The recommendation to use 4 6vdc batteries is spot on.

I'm not sure what the distain is all about in this thread for AGMs, but AGM batteries are hands down better than flooded wet-cell batteries. They have a lower internal resistance which means reduced heat during discharge cycles, and reduced time for charging. AGMs also have a lower discharge floor of 80% compared to 50% for flooded batteries; HOWEVER, you should never discharge an AGM below 50%. They are maintenance free and don't have to worry about spills or off-gassing of noxious fumes, although AGMs can off-gas if over-charged. Speaking of over-charging...this will kill an AGM battery which is why it's important to have a reliable charge regulator. (Honestly, I don't know of anyone with a boat that doesn't use a regulator...but I suspect there may be a few fools out there.) Finally, although AGMs cost more than flooded batteries, they also last longer. I had a set of Lifeline AGMs that lasted 10+ years. (I replaced them before I left Seattle just to start with a fresh set as I set out across the Pacific.)

Also, as others mentioned with your setup of 400W solar and in Florida you should not have a problem running a refrigeration unit, even with 200Ah if nothing else was running. But, IMHO 200Ah for a house battery on a 39' boat is way under-powered. Again, if you go with 4 - 6vdc Lifeline AGM batteries (2 in series, and the 2 sets in parallel) you will have 440Ah of available power. By using too small of a battery bank you are likely discharging your 200Ah batteriy bank below it's discharge floor causing them to fail prematurely. That's just a guess in your case, but I've seen this happen multiple times by undersized battery banks on boats.
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Old 10-08-2022, 14:18   #10
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Re: Assistance with Battery choice

We use 6 volt golf cart batteries (Deka/Penn ~ $120 each) with about 600 watts of solar. It runs the boat fine and we are live aboards so use fridge, freezer, lights, and fans. Something sounds wrong or maybe the batteries were just toast? Our batteries last 6~7 years.
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Old 11-08-2022, 07:50   #11
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Re: Assistance with Battery choice

If the boat lacks "floor space" for 4 of the 6V batts, (like a T105,) but does have space for increased height, an option is the "J-305" size unit.
They are ~2>2-1/2" taller and have a lot more capacity, but they do cost more on a dollar-per-amp hour basis.
I used to have 4 of them for the house bank, 2 Trojans and 2 Rolls.
The Trojans went 9 years, the Rolls 10.
On a "bean counter" basis the Trojans were a better deal, Rolls claims higher amp hour capacity but that comes at the expense of less "top water" above the plates, and so requires more frequent monitoring of water levels.
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Old 11-08-2022, 08:09   #12
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Re: Assistance with Battery choice

I believe that the Deka batteries are mostly made by East Penn, who also make a number of other brands. https://www.eastpennmanufacturing.com/


The advice that you should better understand what is going on with your electrical system as a whole, is good advice.


Flooded batteries are no longer recommended for sailboats following the 1998 Hobart Race, where six people died. Among the factors that led to their death was failure of the flooded batteries following a rollover/inversion of the boat, which led to inability to contact rescue resources via radio.
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Old 11-08-2022, 08:57   #13
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Re: Assistance with Battery choice

Before buying batteries, do a good audit of what is drawing power.

Ideally an amp-hr meter on the battery would be best but even just getting the amps to each device and estimating the duration it's operating is better than random battery suggestions. You might have other stuff beyond the fridge using power...or the fridge may not be functioning properly and drawing excess power.

Then once you know what you need, you can back calculate what you need in terms of battery bank and solar.
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Old 11-08-2022, 09:22   #14
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Re: Assistance with Battery choice

As stated above a few times, your solar charging isn't working correctly.

I have two house group 31 agm, run the fridge, fans, lights and easily charge with 330 watt rigid panel.

Are your panels shaded, or do you have many cloudy days in a row?
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Old 12-08-2022, 14:27   #15
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Re: Assistance with Battery choice

bensolomon - My panels are almost never shaded. I'm in Miami FL and keeping the son at bay is quite a challenge.
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