More than 4 12v batteries in a Bank?

72 Posts
Jul 16, 2009 08:37 pm
More than 4 12v batteries in a Bank?

What prevents me from connecting more than 4 12v batteries, in one 12v bank?

I currently have 4 12v, in a 12v bank, and would like to connect either 2 or 4 more to the same bank ... keeping it at 12v.
8 Posts
Jul 16, 2009 09:06 pm
Re: More than 4 12v batteries in a Bank?

What would keep you from stacking more than 4 batteries? 
72 Posts
Jul 16, 2009 09:22 pm
Re: More than 4 12v batteries in a Bank?

I'm not sure .... but I've been advised not to do it.
something was said similar to this:

"... you don't want to have too many parallel strings. Four is the max. "

I'm guessing that it is to prevent too much power being pulled from the end of the string ... but wouldn't a bus bar or tying at a center point fix that?
8 Posts
Jul 16, 2009 09:30 pm
Re: More than 4 12v batteries in a Bank?

Never heard that not to say its not true. I have 8 100 amp hour 12v batteries in my bank. Have the positive for inverter and charger on opposite ends than their negs. Thought about it pulling off one battery more that the rest and killing that battery so did it that way so it has to pull through the bank and charge through the bank also. You have any links to that data?
72 Posts
Jul 16, 2009 09:36 pm
Re: More than 4 12v batteries in a Bank?

The way you are doing it sounds like a good compromise, and I would think it would help even the stress out.

I don't have any links, just a couple of different people advised me not to do more than 4.

I have not been able to find any thing via google that supports it yet ... so I'm hoping this discussion will clarify the concern ... and the options.

how long has your 8 battery bank been live?

mine would be just about identical to yours ... I have 4 105ah 12v in place, and want to add 4 more of the same batteries, and either tie at the opposite ends or the centers of the two sets of 4.

« Last Edit: Jul 16, 2009 09:37 pm by Keith Birchfield »
8 Posts
Jul 16, 2009 09:52 pm
Re: More than 4 12v batteries in a Bank?

A few months now I have been at over 4 . Been adding 1 or 2 a month. Gel cells are expensive and thats what im using due to having my setup in the house. Up to 8 for about a month now. I found this link in another post on here and they are saying you are good up to eight doing it like I done mine. Did find out off that I have my charger hooked up to wrong terminals though I thought you shouldnt hook it up to same ones as inverter but guess I was wrong.
72 Posts
Jul 16, 2009 10:01 pm
Re: More than 4 12v batteries in a Bank?

Excellent link ... Thanks!
49 Posts
Jul 16, 2009 11:18 pm
Re: More than 4 12v batteries in a Bank?

  Im using 16 105 amp gels 4 rows in series and 4 rows parallel  for 48volt. works great also have outback controller going in one row and out the last row to the inverters.
72 Posts
Jul 17, 2009 05:44 pm
Re: More than 4 12v batteries in a Bank?

What does this statement mean:

"If you parallel more than three strings of batteries, you risk shortening battery life due to uneven charging1."

in this article:

and it references this:

1A great article explaining the rationale behind this paralleled string limit is available in Home Power Magazine issue 114: “Top Ten Battery Blunders.”]]

which mentions:
The problem is that when current splits between parallel strings, it’s never exactly equal. Often, a slightly weak cell or terminal corrosion will cause a whole battery string to receive less charge. It will degrade and fail long before other parallel strings.

But, help me out here ...

A 'string' is a set of batteries connected in a line ... positive to positive and negative to negative ... right?

So, If I have 8 batteries connected this way ... its only one string ... right?

And then to 'help' even out the draw and charge, just connect the positive to one end of the string, and the negative to the other end. ( or tie all positives together, and all negatives together )

Another reference to "no more than three:
« Last Edit: Jul 17, 2009 07:54 pm by Keith Birchfield »
Jul 18, 2009 04:59 am
Re: More than 4 12v batteries in a Bank?

Think in terms of how a battery is built and how it works.
The most basic battery is a nominal 2 volt cell.
A 12 volt nominal battery is built as 6 - 2 volt cells in series. One cell can go bad and this disrupts the line of chemical exchange in the rest of that battery and any other battery that might be in parallel with it. If several 12 volt nominal batteries are wired in parallel this increases the chance of a disruption caused by just one faulty 2 volt cell within one 12 volt battery. One bad apple does spoil the whole bunch in this case. Its a major chore but, one could periodically remove the wiring harness from a parallel "string" of 12 volt nominal batteries and check each one individually to insure that each battery is up to "par" or, build the same amp hour capacity battery with 6 large 2 volt nominal batteries and if there is a faulty cell you'll know it right away. Its my opinion there is no right way or wrong way, one just makes sacrifices of one aspect in the hope of gaining in another aspect. Of course if a sacrifice is made in order to, lets say, save money in the here and now, then one has to know what the consequences are going to be and follow through to the end. But you already know this, thats why you are here trying to find out those consequences. Seeking the opinions of others that have been there and done that.

The amp hour capacity would come in to play but I would say, if its possible, use 6 - 2 volts cells. Fewer cells to fill, fewer connections to maintain, if one goes bad, you know it right away. But then I don't have a lot of free time one my hands. If I did, I might say just the opposite and possibly save some money in the here and now with 12 volt batteries even though it might cost me more over the long haul if one cell in one battery goes dead and I don't catch it in time to save the others from being dragged down. 

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