Ok, Thoughts re: Battery Capacity

[Rick D]

So, thinking through replacement of my Sam's Club six volt golf cart batteries. They have been in for three years. Getting a bit weak-kneed. They get some heavy use, so three years is typical; maybe four if I push it.

Anyhow, I see Sam's has a larger capacity option; probably like a Trojan T125 vs. T105. It is 232 AH at 20 amps vs. 208, a difference of 12%. The price in SoCal is $110 vs. $80, or 37%.

So, here's my point. The additional capacity would be nice for a single over night race. But that only a couple of times a year. The rest of that use is on our mooring where I rely on solar and my Honda to handle the 120 amp daily draw. So, it seems to me that it makes no difference. Once I blow through the capacity, it will take the same amount of charging to put AH's back in regardless of which batteries are in the bank. It's just a matter of running the Honda longer to charge the larger capacity bank. I'm still only going to get X from the solar regardless. Thus, the $80 ones will seemingly serve me just as well.

OK, so is this too simplistic? If so, what am I missing?

 

[Benny17441]

I concur with your assesment. I size the battery bank to serve my usual needs plus a little reserve. For those few outings where more capacity is needed I just push the bank a little farther. 50% of capacity is not a magic number and pushing the batteries on a couple of occassions will not significantly shorten their life. I avoid unnecessary cost, weight and having to upgrade the charger. A slightly shorter charging time is a significant plus when on the move. Go for the $80 ones, nothing wrong with a proven system.

 

[Stu Jackson]

I agree. As long as they're within your energy budget, only difference is either longer or earlier charging, right?

 

[Don S/V ILLusion]

I contemplated the same choice Rick and went with the T125s. My reasoning being similar to your thoughts but when I thought about the down the road loss of capacity as they age, I figured the slightly larger ones made sense ynot based on economics but rather for whatever peace of mind in thinking they might last a bit longer. How's that for a run-on sentence?

 

[Squidd]

Please correct my math and terminology (that's why I'm asking the question)...

The T-125s are 232 a/hr @ 20 amp.... <@ 6 v.>...when you connect them in series(?) do you get 464 a/hr @ 20 amp <@ 12 v>...? Or 232 a/hr but "last longer"...

For energy budget purposes...

 

[JoeWhite]

Squidd - when you connect them in series the voltage goes from 6 to 12 volts but the capacity remains the same. If you connect the two 6 volt batteries in parallel - then the capacity will double.

 

[Chef2sail]

How large is you solar array. Does it have the capacity to keep them charged and bring back to 100% or are you always around the 85% mark. With a bank of 6-6 volts. You have approx 630 ah and 315 useable. I am assuming you start at If you 100% but then you can only can get them charge at 85% then its 268 usable, barely two days for you.

I am suprised you only get 3-4 years. Do you desulfate the bank periodically?

Your 120 daily diet seems high. Do you have two reefer compressors? If you have a large enough solor array and can bring back to 100% easily you may be a candidate for AGMs. We have 6-6 volt Lifeline AGM, but our usage allows us to bang a charge in them enough to keep them at close to 100% charged levels justifying their cost over time. They have a good acceptance rate.

Maine Sail ( I am assuming you will read)...how do people on moorings desulfate their batteries if they dont have availability of a shore charger? Can they adjust the solor/ alternator regulator to push in a higher charge?

Dave

 

[Sumner]

How big is your bank? Two 6 volt or four, or more?

Let's say it is four. Then the cost difference is $120. If your batteries last 3 years then that is $40 a year extra for better batteries and now they might go the 4 years and that would pay for itself there.

We finally got back to the Endeavour in Florida and I'm going through the same deal. Trogan's (225 a/h) are $98 here and the PowerTron's (210 a/h) are $73. The battery guy claims the PowerTron's are made by Trogan but have thinner plates. With 4 batteries in the bank I'm only picking up 30 a/h and then only 15 a/h if I don't draw them down past 50% so amp/hour wise there is not much to be gained with the Trogan's. If the plates are thicker and we can get another 1-2 years out of them then I think we are ahead with the Trogans. By then we might of sold the boat.

We have 480 watts of solar...

http://purplesagetradingpost.com/sumner/endeavour-electrical/electrical-index.html

...on the boat and daily loads in the 50-60 amp/hour range so I'm hoping these batteries will go the life of the boat for us since they won't be drawn down more than 15%-25%.

I think we will pay the extra $100 or so upfront and hope that we won't be replacing batteries if we take care of them,

Sum

P.S. Curious as to what you are using to get the daily loads that high?

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[Rick D]

Specifics

How large is you solar array. Does it have the capacity to keep them charged and bring back to 100% or are you always around the 85% mark. With a bank of 6-6 volts. You have approx 630 ah and 315 useable. I am assuming you start at If you 100% but then you can only can get them charge at 85% then its 268 usable, barely two days for you.

I am suprised you only get 3-4 years. Do you desulfate the bank periodically?

Your 120 daily diet seems high. Do you have two reefer compressors? If you have a large enough solor array and can bring back to 100% easily you may be a candidate for AGMs. We have 6-6 volt Lifeline AGM, but our usage allows us to bang a charge in them enough to keep them at close to 100% charged levels justifying their cost over time. They have a good acceptance rate.

Maine Sail ( I am assuming you will read)...how do people on moorings desulfate their batteries if they dont have availability of a shore charger? Can they adjust the solor/ alternator regulator to push in a higher charge?

Dave

Dave, I have four. The solar array totals 166 watts. I have both a mooring and a slip, so they do get back to 100%. I equalize annually. I have a separate frig & freezer compressor. Everything else is low-draw. When on the mooring, I take it up to 80-85% with the Honda whenever if falls to 50%.