What is the logic using 6v batteries in series

Why is 6v batteries in series to make 12v so common? Why wouldn't one just get a 12v to start with, half the space... what am I missing?

Seevee said:

Why is 6v batteries in series to make 12v so common? Why wouldn't one just get a 12v to start with, half the space... what am I missing?

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Golf cart batteries are one of the best deep cycle alternatives available. They are designed for incredibly demanding use. A golf course will charge the batteries up overnight, then they get run during the day until almost dead, then get recharged again. These batteries are designed to take that abuse. They are also relatively plentiful and inexpensive. So they often are the best value per Ah compared to other types of batteries. There is no advantage to 6v, it is just that these batteries are only available in 6v.

Would you say that they are as robust as 2V batteries, which are generally rated to 80% depletion?

Also to get the equivalent ampacity in 12V, the battery would weight 120+ lbs rather than 60+ lbs for 6V. Moving the 6V batteries around is not so challenging as moving 4D or 8D equivalents.

2v will require a bunch of jumper cables or links. Lots of connections.

FlyWright said:

Also to get the equivalent ampacity in 12V, the battery would weight 120+ lbs rather than 60+ lbs for 6V. Moving the 6V batteries around is not so challenging as moving 4D or 8D equivalents.

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Bingo!! Winner, winner, chicken dinner! Why lift 120lbs when you can split it in half.........

One difference between 6 volt and 12 volt banks arises when you build large capacity (measured in Amp-Hours) banks. Lets take a hypothetical bank using 4 - 6 volt GC batts (6V bank for short) and another using 4 - 12 volt batteries (12V bank) of similar physical size. The 6V bank will have 2 batteries in series to make 12 volts and then a second set of 2 in parallel to the first. There is only 2 current flow paths through the entire bank. The 12V bank will be 4 - 12 volt batteries all parallel to each other. There will be 4 current paths through the bank. All is well and good when the banks are new. As the batteries age and the internal resistance increases, the current though the bank will seek the path of least resistance. This leads to unequal current flows though the 12V bank. Some of the 12 volt batteries will be chronically under charged, some over charged, leading to an overall shorter bank lifetime.

6 golf cart batteries will fit in the same space as 2 8D's. The two 8D's will have a total amp hour capacity of about 440 amps. The six golf cart batteries will have a total amp hour capacity of about 630 amps. About 50% more capacity in the same space and, as already stated, easier to handle.

Two other big factors are their robust build and deep cycling ability...at least in the lead acid family.

Wonderful true deep cycling 12V units do exist, but only from a handful of mfg, never in mass retail channels.

99.9% of the 12V labeled "marine deep cycle" used on most (ly smaller but also even large yachts with ignorant owners) are IMO fraudulently labeled, poor choice for deep cycle use.

​To save money up front, the best value by far is Duracell (actually Deka/East Penn) GC-2 from BatteriesPlus or Sam's Club deep cycle golf cart batteries, 2x6V.

If you KNOW your infrastructure and usage patterns will allow these to last 5-7 years, only THEN is it worth spending a lot more per AH for higher quality to get 12-14 years at a time.

Ski in NC said:

2v will require a bunch of jumper cables or links. Lots of connections.

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Isn't a 12 volt battery just six 2 volt cells rigged in series inside the case?

Egregious said:

Isn't a 12 volt battery just six 2 volt cells rigged in series inside the case?

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Yes, but you don't have to buy and install the cables and maintain the connections.

dhays said:

Yes, but you don't have to buy and install the cables and maintain the connections.

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You would and that's why I wouldn't use 2v batteries and reinvent the wheel. GC yes, because of the weight.

Now, when ya wanna get serious.... just 2 off these 6 volt batteries will do the job.

What kind of batteries of batteries are those? ^

I just replaced my house batteries. I use 6V GC batteries because of the weight. It took me 3 hours of backbreaking work to get the 4 6V batteries out and another 2.5 hours to get the new ones in. If they were 8D's it would have been impossible for me to get them in or out.

Nightsky said:

What kind of batteries of batteries are those? ^

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They are Rolls, made in Canada. They are heavy, but rated at 820 amps each.

"Would you say that they are as robust as 2V batteries, which are generally rated to 80% depletion?"

All WLA batts come with a chart.

Deplete then to 50% and you can do it a certain number of times, go all the way to 80% down and you get to do it many times less.

6V are preferred over 12V as the internal spacing allows for more lead , and fewer spacers.

Its the lead that does the work, not the plastic.

With half the number of fill caps 6V watering is faster.

Also the 6V golf carts are made in higher numbers , so are cheaper,per amp hour.

FF said:

6V are preferred over 12V as the internal spacing allows for more lead, and fewer spacers.

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The top vendors have excellent 12V batteries that last as long as the lower-voltage equivalents. It's not an inherent difference.

FF said:

Also the 6V golf carts are made in higher numbers, so are cheaper, per amp hour.

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In a mass retail context, they are all that's available in true deep cycling, and yes those Sam's Clubs are lowest up front investment.

But once you're buying from the top-shelf vendors, not true at all.

Decisions once you're in that segment are based on design factors like serial/parallel layout, longevity and size/weights, not so much price.

Yep...until the top of the line batteries have an issue and you have to replace them, even one much earlier than the normal cycle.


Especially purists who say replace the bank at once.


That is a good argument for individual cells....if you can afford the whole deal up front and down the road.


Many people don't keep their boats for the real payback period...so running the numbers is kinda theoretical anyway.


The average boat here can carry enough inexpensive golf cart batteries to survive just fine. At some point, solar and wind is cheaper than more batteries.

An old boating guru friend of mine said many years ago: Electricity is black and heavy..
Back then practically all batteries were black, so more heavy = more electricity.
I'd rather carry several 6v GC around than one 8D.

I'm just saying the GC choice is the result of practical reasons like those, not any inherent technical advantage.

How true...but you don't need a space shuttle when an ultralight will do....


Tech often buys dreamers, like lures to fisherman (not fish), realists and experience but the best bang for the dollar that still suits ones needs.


Not saying people shouldn't support and build tech...but like the new hybrid cars...it's usually the people that can afford getting over the hump...not us just getting by boaters.


And sometimes it is us filling the cruising ranks and enjoying it without battery issues, not still working 80 hrs a week.

Even strictly from a practical POV, there are scenarios where investing in a top-notch more expensive bank is worth it financially.

You need to be able to afford the up-front of course.

And you need the usage pattern, knowledge and infrastructure in place to ensure you're getting the extra longevity you're paying for.

If you're not sure of the latter, Sam's GC2 is way to go.

The last time I strained to remove 4D batteries from my boat, I swore it would be the last time. Six volt golf cart batteries because I like not having a bad back.

john61ct said:

Even strictly from a practical POV, there are scenarios where investing in a top-notch more expensive bank is worth it financially.

You need to be able to afford the up-front of course.

And you need the usage pattern, knowledge and infrastructure in place to ensure you're getting the extra longevity you're paying for.

If you're not sure of the latter, Sam's GC2 is way to go.

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I do know all the right things...or could easily look them up.

...and I know even the best of the best fail straight from the manufacturer...or 6 days after the warranty expires....there are no guarantees and battery insurance is one more insurance off my radar.

Sounds like some of you guys are changing out your batteries every month. The true industrial batteries easily go 10-15 years or more, rated 80% at 18 years for example. So perhaps it's worth having high quality even if it weighs 160 lbs.

makobuilders said:

Sounds like some of you guys are changing out your batteries every month. The true industrial batteries easily go 10-15 years or more, rated 80% at 18 years for example. So perhaps it's worth having high quality even if it weighs 160 lbs.

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Well.....the vast majority of boaters I know use golf cat batteries for a reason.

Lack of knowledge may be it...but there are some pretty smart engineers and boat business guys are in that crowd.

Any specific batteries you have on the tip of your tongue with those generous life spans?

No, not lack of knowledge. Sourcing good value golf cart batteries from Sam's, Costco, Walmart, etc., is great if you have access to those stores. In doing my own pricing I have compiled the comparison in the chart below.

Regarding my particular selection, I have spec'd out an entire house-load package (solar, MPPT, batteries, inverters) from Everexceed in China. They are pricing now. For batteries I am referring to their "Tubular OPzS" 2 volt flooded cell. At 80% discharge they still have a life of over 2000 cycles.

I've been unable to find the proper graphs for Trojan, but in general the golf cart batteries appear to offer about 600 cycles @ 80% DOD, 1500 cycles @ 40%DOD.

If you have other info please share.

for me, 220 ah/$320 for 2 Trojan golf cart batts....that's less than $1.50 per ah.


but nothing on that chart suggests other than theoretical discharge and amount of cycles a certain number of years longevity.


as I posted before, reasonable consumption and constant topping off with solar negates deep discharge needs or large banks.


if I sat at anchor a lot in a cloudy area, maybe I might consider batteries that cost that much.