Choosing house batteries

[JV II]

Here’s one for the engineers:
Which would be the better battery set-up for a house bank?:

OPTION 1:
2 Interstate U12VGCUTL 12V Golf Cart batteries wired in parallel
Each battery has 155 Ah capacity at @20 Hr, reserve capacity of 292 min at 25A draw, 77 min at 75A. Each weighs 90 pounds and measures 13 5/8 x 7 1/16 x 11 3/8.
This set-up will yield 310 Ah capacity @ 20 Hr, a reserve of 584 min at 25A draw, 154 min at 75A draw.

OPTION 2:
2 Interstate GC-2 6V Deep Cycle batteries wired in series
Each battery has 232 Ah capacity at @20 Hr, reserve capacity of 474 min at 25A draw, 122 min at 75A. Each weighs 63 pounds and measures 10 1/4 x 7 1/8 x 11 1/8.
This set-up will yield 232 Ah capacity @ 20 Hr, a reserve of 474 min at 25A draw, 122 min at 75A draw.

Here’s the link to Interstate for the stats on these batteries:
http://www.interstatebatteries.com/www_2001/content/products/product_marine.asp

Check my math, but just going by the numbers, it seems that Option 1 would be the better choice. My concern is the construction of a 12V vs. a 6V. There is no information to compare the plate size, number, and design within Interstate and between manufacturers. Is there any reason to believe that the 12V batteries will not last as long as the 6V batteries?

 

[Pirate]

Julia- I didn't look at the specs on your Interstate batteries, but you will want to stay with an AGM battery if you have deep cycle intent. The AGM will be less (no) maintenance and it will last longer than lead acid with deep cycle use. I use the Trojan AGM's for everything now.

 

[Warren]

Matt I would agree that AGM batteries would seem to be the best option but I understand that, unlike lead acid, they cannot be stored below freezing. This is a serious consideration in this climate as I have enough to do winterizing without taking all the batteries home!

Having said that, Julia I will be facing the same decision myself in the new year as the 400DA is a new boat for us and I have to upgrade batteries also. In used 6V. golf cart batteries on our last 2 sailboats with a 2kw. inverters in each (mainly for fast charging at 80-90 amp) and 100 amp alternators. I found them to be extremely durable and reliable. They are designed to be abused and - although I did install energy monitors in both cases with alarms to sound at 50% discharge - they did get MANY cycles in the six years of ownership. Presumably the new owner is still getting good results.

Sorry that I can't offer any insights on 6 volt vs. 12 volt golf cart batteries but I am very interested in this topic and await other opinions. I would also like comments on the freezing question. You are definitely on the right track in my experience!
Warren

 

[Sea Gull]

My last boat had AGM batteries. No problem leaving them in the boat all winter in Connecticut.

 

[Warren]

Thanks for your comment Sea Gull. I asked Trojan the same question today. They e-mailed me literature on the subject and did confirm that in their opinion AGM batteries are more able to withstand sustained below freezing temperatures than lead acid. Of course, it is always prudent to give stored batteries a float charge periodically at any temperature.

Sorry about this aside Julia. After settling this issue, for me it will come down to cost. How many $ spent to get the required AH for the house bank given any space/weight constrains. Based upon what I know now if AGM batteries are affordable they will be first choice for me.
Warren

 

[Hampton]

Just bought 4 AGM's this Summer and they seem to be great. Others have said that they last 5 - 6 years. Take that cost into account, and they're maintenance FREE!

 

[JV II]

I just got the quotes for the Interstates from the dealer. $125 for the 6V Deep Cycle and $250 for the 12V Golf Cart. The Interstate website did not indicate that the 12V was an AGM, but at that price it should be! The website lists weight wet and dry, so it is probably a lead acid. Why the heck anyone would pay 100% more for 1/3 more reserve is beyond my comprehension. How much did your AGMs cost and what are the specs? I know I can get Rolls 225Ah lead acid 6V for $210 (less than the Interstate 12V). Rolls seems to have the best reputation, design, quality from what I've read. They are also the most expensive. Trojan make a nice T105 225 Ah 6V for a price under $150. They are highly rated by consumers. It seems like the quality and durability of any "common" manufacturer like Interstate is a gamble. I'm steering toward 2 6V golf cart batteries from Trojan, Rolls, or some other commercial manufacturer (Deka?)

 

[Hampton]

Right at about 217 each, delivered, over the internet. Most places are within a few bucks. (Optima D31M Blue Top Deep Cycle Marine, Battery 8052-161 D31M $217.60 $870.40) http://bigtimebattery.com/store/index.html

 

[fwebster]

Why would freezing temperatures affect AGM's..................they are dry and do not use a liquid electrolyte.

 

[Warren]

The surveyor suggested that I buy Optima Blue Top 12V. 155AH@ OR Deka L-A as replacements and to remove AGM batteries in winter if I make that decision. ???
Warren

 

[Jaws]

For what it's worth:

If you are interested in AGM batteries, Powerboat Reports (remember that was the monthly that bashed SR cored boats) did have an interesting comparison in their March 2006? issue on AGM's. Trojan was rated best buy and Mastervolt were top performers in their testing. Optima was also a good choice.

The periodical (PBR) is now defunct but it was useful at times. It was also controversial in its editorials as any Sea Ray owner knows.

I used Trojan AGM with good success (three group 31-starting and house, and one 27 for the genny).

James