4@12v = 24v

Hi,

The real answer is "It depends". If you are going to use a largish inverter and run it "flat out" (in my case about 250 amps) then a series connection of batteries may unlove you, unless you have pockets deep enough for 850 amp two volt cells. (see what I mean? It DEPENDS). Since I have a beer budget 12 volt jars in parallel meet my (rather extreme) needs.

It is not the cost of the batteries that keeps me from going to 2 volt jars. It is the modifications I would be forced to make to the RV.

If I were in 2oldman's shoes I'd sure look at AGM 12 volt in series parallel with disconnect switches between the twin banks. Normal operating would be all four wired in a balanced manner. Switching would allow him to condition one set of batteries while using the other.

In my shoes, I'll possibly replace all eight batteries (counting the chassis) so that one charging profile will fit all of them. If LI comes on the scene perhaps AGM's may fall in price?

2oldman wrote:

ken white wrote:
Define better...

I can't.

Me either...

:)

ken white wrote:
Define better...

I can't.

Salvo wrote:
Sounds like another parallel vs. series discussion to me. ;-)

As they say, you're only as strong as the weakest link in a series string. Or, one rotten apple can spoil the series string.

Which scenario is better: 6 batteries in parallel or in series when one of the batteries has 3 times the internal resistance as the others.

Sal

There are advantages and disadvantages to both. A battery that has a shorted cell (fairly common failure mechanism in older batteries) will become a sink and can drag down an entire bank of parallel-wired batteries. A shorted cell in a series string will simply reduce bank voltage by ~2 volts.

Personally I would choose series over parallel. Assuming you start will all new batteries of the same capacity, and you maintain them properly, there is probably less of a chance of an imbalance developing in the first place.

2oldman wrote:
Which is better when nothing is wrong? Probable answer: it doesn't matter.

Define better...

There are so many variables in application that better is a relative term based on specific needs at a decision point.

Good, clear, definitive answer, huh?

:)

Which is better when nothing is wrong? Probable answer: it doesn't matter - although I do find it interesting that a battery itself is cells in series.

Sounds like another parallel vs. series discussion to me. ;-)

As they say, you're only as strong as the weakest link in a series string. Or, one rotten apple can spoil the series string.

Which scenario is better: 6 batteries in parallel or in series when one of the batteries has 3 times the internal resistance as the others.

Sal

lorelec wrote:
And higher voltage battery banks usually have more batteries wired in series, which forces each of them to share an equal amount of current. Current sharing in parallel batteries can become imbalanced (especially as the bank ages), which leads to shorter battery bank life and reduced overall capacity.

Higher voltage is done primarily to reduce wiring losses or allow the use of lighter gauge wire. Higher (input) voltage inverters also tend to be a little more efficient. And higher voltage battery banks usually have more batteries wired in series, which forces each of them to share an equal amount of current. Current sharing in parallel batteries can become imbalanced (especially as the bank ages), which leads to shorter battery bank life and reduced overall capacity.

I also just like to try new things. Makes for some good discussion on here! That, and my Prosine bit the dust !!

I changed my mind about 24v being better.

The OP did it for the inverter wiring, and has an elegant set-up that solved his problem, but I don't have that problem.

It does not increase your capacity for how long you can run things.