Battery Size with the same AH...

[MedSailor]

I've noticed that some golf cart batteries can pack a whole lot of amp hours. A pair can have even as many as a 4D. If you have the space, is there some reason that a physically larger battery would be better? Do you have more of an electrolyte reservoir, are the plates further apart?

Any reason a single, say, 210AH 4D would be a better choice than 2 210AH golf carts?

MedSailor

[btrayfors]

Nope, unless you're planning on back surgery :-)

In fact, a great solution if you've got the space and the bucks is the Rolls/Surette big 2V cells -- six of them in series to make the 12V you need. Each cell is manageable in size and, in the event a cell should die, it can be replaced without replacing the whole shebang.

And...they normally provide 10-15 YEARS of service!

But, pricey...

The golf-carts are a cost-effective solution for many/most cruising sailors, though!

Bill

[chef2sail]

We have a bank of 6- 6 volt Lifeline AGMs. They have an even smaller footprint than most 6 volt batteries ( golf cart ) and each pair has 245ah giving us 735 ah at about 50 % drawdown 360 ah. Our electrical diet is about 90 ah per day with most of that being the alder barbour super cold machine. Replacing and beefing up the friges insulation really helped cut downthe draw from the alder barbour. We also started replacing lights with LED as they burn out.

These AGMs charge quickly and can be arranged on their sides if necessary. I highly recommend them.

Dave

[mitiempo]

I think (along with many others) that golf cart batteries are the best value of all. Yes they do require a few minutes of maintenance every month. But that is a small price to pay for reliability and longevity. AGM batteries have advantages - a bit smaller footprint, faster charging, and less maintenance but this comes at a price. For this higher price you don't get more amp/hours or more cycles before they need replacing. They require precise charging, have to be fully charged every 2 or 3 weeks, and give less cycles than a comparably built wet cell battery. Wet cell batteries can be abused on occasion and the level of fluid brought up to where it should be but AGM batteries are less tolerant. Below is a chart from Trojan Batteries showing life cycles of their 6 volt batteries (right column). The T105 is shown at 754 life cycles - more than any other Trojan 6 volt and more than twice that of most of their 12 volt batteries - all deep cycle. Dollar for dollar I don't think they can be beat.
Brian

[MedSailor]

I appreciate the opinions about AGM vs Wet but I that particular question has been debated before, I think.

I was hoping to address the question of if there is a difference between large and small SIZED batteries of approximately the same AH.

MedSailor

[erps]

I was hoping to address the question of if there is a difference between large and small SIZED batteries of approximately the same AH.

small sized batteries with a similar AH capacity of a larger battery are typically a lower voltage, so it takes more of them to make up for the smaller size. As Bill indicated, you can buy a wet celled battery that has 600 or more amps in it which is still small enough to man handle, but it takes six of them in series to make a 12 volt bank.

[MedSailor]

Originally Posted by erps

small sized batteries with a similar AH capacity of a larger battery are typically a lower voltage, so it takes more of them to make up for the smaller size. As Bill indicated, you can buy a wet celled battery that has 600 or more amps in it which is still small enough to man handle, but it takes six of them in series to make a 12 volt bank.

Allow me to explain my question a little more clearly, with an example. Dyno batteries are a high quality battery. If you put together 2 x 6Volt golf carts you end up with 235AH of capacity at 12 volts.

IF you buy one of their 8D batteries you end up with 240AH at 12Volts.

Specifications here: Deep Cycle

Why is it that you get the same amount of AH when 2 golf carts are about 1/2 (or less) of the physical size of one 8D? Is there any inherent benefit to the larger battery? Possible theories as to why the 8D might be better include: more electrolyte reserve, or plates spaced further apart which would help with sulfiting.

Honestly I don't know why the 8D is so much larger than 2 golf carts with similar voltage and AH capacity. My question is if there is any advantage to the larger battery.

MedSailor

[mitiempo]

I don't think so. Considering number of cycles, amp/hours, price and ease of handling a golf cart 6 volt like the Trojan T105 is the winner as far as I can tell. I don't think an 8D can compare.
Brian

[erps]

Why is it that you get the same amount of AH when 2 golf carts are about 1/2 (or less) of the physical size of one 8D?

When I do the math (rounded down, no fractions) I get 1400 cu in for two golf cart batteries and 1980 cubic inches for one 8D. I understand your question better now. If there was no advantage for a large battery like an 8D, then why are they still being sold? I dunno. Simpler maybe. No extra battery cables to hook up?

[bubb2]

It's popularly believed that 6 volt batteries are better for deep cycle power applications than 12 volt batteries, but it isn't true. This myth likely developed from the fact that golf carts use 6 volt systems. Because golf cart batteries were the only deep cycle batteries widely available for many years, the best way to obtain good 12 volt deep cycle power was to connect two 6 volt golf cart batteries in series (or more batteries could be connected in a combination series and parallel configuration for higher voltages like 24 volts or 36 volts.) The effectiveness of that approach owed entirely to the design characteristics and quality of the batteries used, not to the fact that the batteries used produced 6 volts.

In reality both 6 volt batteries and 12 volt batteries are simply built from 2 volt cells; if a battery is built with three such cells, it's a 6 volt battery. If a battery is built with six such cells, then it's a 12 volt battery. To make a 12 volt system by connecting two 6 volt batteries in series is to do nothing more than to build a 12 volt battery with two cases and external interconnection. In fact, every cable end connection results in some efficiency loss, so the two 6 volt batteries, because they must be connected by a cable, will be slightly less efficient than the 12 volt unit.

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