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Old 10-08-2016, 04:36   #1
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Multiple battery banks or one big one

I am in the process of installing new house batteries. I have four 6v golf cart batteries in two banks. Is there any real advantage to having two separate banks and using my A/B switch to use them one at a time or have one big bank? The one big bank is easier to charge and maintain but causes an issue if I get a bad battery as I have to replace them all. Comments ?
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Old 10-08-2016, 05:05   #2
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Re: Multiple battery banks or one big one

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Originally Posted by Steve O View Post
I am in the process of installing new house batteries. I have four 6v golf cart batteries in two banks. Is there any real advantage to having two separate banks and using my A/B switch to use them one at a time or have one big bank? The one big bank is easier to charge and maintain but causes an issue if I get a bad battery as I have to replace them all. Comments ?
Living off the grid mostly I like having the ability of splitting the 4 6v I have into 2 so every few days 1 pair can get a really good charge direct to solar. And equalize them separately.
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Old 10-08-2016, 05:06   #3
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Re: Multiple battery banks or one big one

Go for one house bank. This was settled years ago

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Old 10-08-2016, 06:10   #4
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Re: Multiple battery banks or one big one

One big bank and a separate starter battery.

And use 12 V not 6 V units (if your boat is 12 Volt wired) - bad battery? remove the bad apple from the bank and keep on going.

Must be some US 6 Volt taboo or something?

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Old 10-08-2016, 06:38   #5
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Re: Multiple battery banks or one big one

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Originally Posted by barnakiel View Post
One big bank and a separate starter battery.

And use 12 V not 6 V units (if your boat is 12 Volt wired) - bad battery? remove the bad apple from the bank and keep on going.

Must be some US 6 Volt taboo or something?

b.

I have one big bank myself, actually it's not, it's two banks, but i leave the battery switch to Both, which I believe accomplishes the same thing?

Oh and 6V Golf Cart batts are simply the best battery for the money there is, and in the US anyway most deep cycle 12V batteries, aren't. I used to say there were no real 12 V FLA deep cycle batteries, and was corrected cause Rolls makes one

I think the concern is that sometimes a bad battery will kill the whole bank, if your bank is split, then it will kill only one?
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Old 10-08-2016, 07:02   #6
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Re: Multiple battery banks or one big one

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One big bank and a separate starter battery.
This is generally acknowledged to be the best, most efficient and practical setup.

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Originally Posted by barnakiel View Post
And use 12 V not 6 V units (if your boat is 12 Volt wired) - bad battery? remove the bad apple from the bank and keep on going.

Must be some US 6 Volt taboo or something?

b.
Several reasons to use pairs of 6V batteries in series instead of 12V batteries. As A64 mentioned

- Almost all 12V batteries sold as deep cycle are only kind of deep cycle, more like medium cycle batteries. I guess the RR is an exception and there may be others but in general you're not getting true deep cycle 12Vs.
- The most bang for the buck. At least in the US you can buy excellent quality, true deep cycle 6V batteries for under $100 each. A pair of GC2 golf cart batteries will give you about 210-230 amp hours (depending on the brand and the manufacturer's rating method) at 12V for under $200.


Another big factor (at least for me) 6V GC2 size batteries are a lot easier to carry around than a single 12V "deep cycle" battery. As my back ages (the rest of me has stayed young ) that difference has become more important.
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Old 10-08-2016, 07:05   #7
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Re: Multiple battery banks or one big one

Several reasons to have one large house bank. For one it's easier to manage charging and loads. The biggest positive is with two smaller banks you end up running down one bank to a lower state of charge than you would if they are combined into one large bank. Better for the life and health of the batteries to not discharge them to a the lower SoC.
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Old 10-08-2016, 07:07   #8
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Re: Multiple battery banks or one big one

I have 2 banks with the switch normally set to to only 1 bank, I can switch to both but I don't. I run only one bank at a time and switch every 2 weeks or so.

They are 6V Golf Cart batteries.

Had Trojans and dumped them. Dollar for dollar, Walmart golf cart batteries are the best bang for the buck.

I once ran one of my banks flat..... 1.2 volts.... OUCH...

Carefully coaxed them back using an older car charger. ( took 2 days ) Got them up to 11 volts and put them on the 100 amp charger/inverter, No problems.

I have two 90 watt solar panels that keep the house batteries "Mostly" charged",,, if I don't go crazy.... but having that second bank available is a great comfort if I do.

I also have a switch to charge them from the alternator, but normally I keep it charging my separate starting and windless batteries.

If my starting and windless batteries wind up both dead, I use jumper cables from bank 2 to handle it. Not a great solution but it's for emergencies only.

So all told I have 11 batteries
4 - 6 volt house - bank 1
4 - 6 volt house - bank 2
1 - 12 volt starter battery
1 - 12 volt windless battery
1 - 12 volt AGM dingy/misc battery ( pretty small so works great for misc stuff)
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Old 10-08-2016, 07:17   #9
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Re: Multiple battery banks or one big one

OK.

I understand 6V sells are smaller and lighter so when the bank is very big, some of us will elect 2 or 6 Volt cells over 12 volt ones.

"One bad apple kills the bank" is only a non supervised scenario. Every time I had a fail (2 times altogether, not much of a sample) I was able to tell there was a battery problem and I removed the bad one without suffering any damage to the whole bank (other than ending up with a smaller bank).

Cheers,
b.
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Old 10-08-2016, 07:55   #10
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Re: Multiple battery banks or one big one

One large bank + a start battery.
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Old 10-08-2016, 08:23   #11
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Re: Multiple battery banks or one big one

Having 2 banks and alternating between them is old school and out dated. The modern approach is a single house bank. This minimizes deep discharging as much as possible. Try to avoid running the batteries down below 50% of the amp hours available on a regular basis.
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Old 10-08-2016, 08:40   #12
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Re: Multiple battery banks or one big one

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Originally Posted by barnakiel View Post
OK.

I understand 6V sells are smaller and lighter so when the bank is very big, some of us will elect 2 or 6 Volt cells over 12 volt ones.

"One bad apple kills the bank" is only a non supervised scenario. Every time I had a fail (2 times altogether, not much of a sample) I was able to tell there was a battery problem and I removed the bad one without suffering any damage to the whole bank (other than ending up with a smaller bank).

Cheers,
b.
So if you have 8 - 6V batteries, you pull two out effectively very similar to pulling a single 12V battery out of the bank. At that point, you decide if it's one or both that are bad and go from there.

While it's not recommended, you can always replace the one bad 6V battery and get back to normal, since you are effectively suggesting the same thing if you have a single bad 12V battery.

The biggest advantage to the 6V batteries is by default they are deep cycle. To my knowledge, no one is producing 6V starting batteries. The 12V are usually just starting batteries relabeled as combination starting/deep cycle.
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Old 10-08-2016, 08:46   #13
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Re: Multiple battery banks or one big one

I have three sets of 6V GC batteries (Sam's Club for over 20 years). Two sets are fed to a common bus bar via a 1/2/both switch and the fwd pair is connected to the common bus bar through a switch. Fuses all around. The fwd bank is tapped to feed a bow thruster, windlass, and a couple of other light loads. No starting battery. All batteries are connected in normal operation, but the switches give me the option of testing each set individually (starting the Yanmar) and isolating a set if something goes south. On rare occasions when I have run the bank down, I have just switched out a set and that becomes the starting set until I can recharge them all.

I have been using this setup for over 10 years (not a live aboard but made several two month cruises). Worked out well for our style of cruising.
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Old 10-08-2016, 08:53   #14
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Re: Multiple battery banks or one big one

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Originally Posted by Steve O View Post
I am in the process of installing new house batteries. I have four 6v golf cart batteries in two banks. Is there any real advantage to having two separate banks and using my A/B switch to use them one at a time or have one big bank? The one big bank is easier to charge and maintain but causes an issue if I get a bad battery as I have to replace them all. Comments ?
If you have an A/B switch, keep it, so you can use it to isolate banks for trouble shooting, but under normal circumstances, keep the switch in the "both" position, to avoid deep discharge of one bank while the other is full.
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Old 10-08-2016, 09:00   #15
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Re: Multiple battery banks or one big one

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Originally Posted by skipmac View Post
Several reasons to have one large house bank. For one it's easier to manage charging and loads. The biggest positive is with two smaller banks you end up running down one bank to a lower state of charge than you would if they are combined into one large bank. Better for the life and health of the batteries to not discharge them to a the lower SoC.
Clearly, I've made my choice. Just heed the topic of how to properly wire up the bank. The world encompassed: Getting the lead in, part 2
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