Extending a part worn battery bank

Willbiker

New Member
Joined
Oct 24, 2020
Messages
14
Hi All

I have 2 sealed lead acid leisure batteries charged by solar. I would like to extend my battery bank by 1 or 2 more batteries of the same brand and capacity however the 2 I currently have have dropped in capacity by about 20%. Are there any disadvantages about adding new identical batteries to a part warn pair of existing?

I probably have a year or 2 more life left in the current pair but would like a little more capacity.

Thanks

Will
 

Wellbuilt

Solar Addict
Joined
Sep 14, 2020
Messages
637
Your new battery’s will be drawn down to the same capacity and they may all die in 2 years .
I all way try to get more capacity in the beginning so when the battery’s are @ 70% I still have enough power
 

boondox

Chief Engineer, RedNeckTech Industries
Joined
Mar 1, 2020
Messages
655
As noted above the batteries will be dragged down some by the old ones. But the old ones will be propped up a bit by the new. Another options is just to beat on the batteries you have until dead and then replace the entire bank.

What are you running with the bank? Is it mission critical, optional or what. That may play a role in your decision.
 

xNYCMarc

Solar Enthusiast
Joined
May 4, 2021
Messages
36
Hi All

I have 2 sealed lead acid leisure batteries charged by solar. I would like to extend my battery bank by 1 or 2 more batteries of the same brand and capacity however the 2 I currently have have dropped in capacity by about 20%. Are there any disadvantages about adding new identical batteries to a part warn pair of existing?

I probably have a year or 2 more life left in the current pair but would like a little more capacity.

Thanks

Will
If you wire the new and old cells in parallel, the amp-hour capacity will be added together. I don't know why people are saying that the cells will be destroyed. People answer questions when they really DON'T know what they're talking about. Perhaps they are just repeating "old wives tales" or whatever without really knowing for sure if what they're saying is true. Of course this wouldn't work with cells in series. ONLY PARALLEL.
In the photos below are my 23kwh battery pack. The grey cells are 6 YEARS OLD Calb 180 cells that I've been daily cycling since November 2015 and have degraded to around 165ah. The black/blue cells are brand new (February 2021) EVE 280 cells. Each old 180 (degraded to 160) cell is in parallel with a new 280 cell. Each two cell pack is in series with the other two cell packs to create a 58 volt pack with each cell at around 3.61 volts when fully charged. I regularly run the pack down to low-voltage-cutoff and blast it with 140 amps of charge current and they stay "perfectly" balanced and the capacity is EXACTLY the two different capacities added together. I'm fully off-grid and have been for the last 6 years.
 

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boondox

Chief Engineer, RedNeckTech Industries
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The OP, (who may be done with this thread anyway) was talking about lead acid batteries. While I at least didn't say the new batteries would be destroyed, it is certainly true that it will shorten the life of the new batteries. Series is indeed more of a problem but parallel arrangements will be affected too.

You are talking about your LFP bank and I have not played mix and match with LFP and so have no experience.
 

xNYCMarc

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Messages
36
The OP, (who may be done with this thread anyway) was talking about lead acid batteries. While I at least didn't say the new batteries would be destroyed, it is certainly true that it will shorten the life of the new batteries. Series is indeed more of a problem but parallel arrangements will be affected too.

You are talking about your LFP bank and I have not played mix and match with LFP and so have no experience.
The chemistry doesn't matter. It's an electrical "problem", not chemistry.
 

boondox

Chief Engineer, RedNeckTech Industries
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I'm going to have to disagree, at least as far as lead batteries are concerned. I've played mix and match many times over the years and have seen many others do it as well. There is no doubt in my experience that mixing old and new batteries will result in a shorter over all lifetime. When I started off grid decades ago, I used all kinds of used batteries, played with de-sulfaters, you name it. I have seen first hand many times the effect of adding beat up batteries to new batteries. I won't say it destroys them but shortens life span for sure. How much effect it has depends on how beat the old batteries are. As lead batteries age their internal resistance goes up and the charge capacity goes down. There are quite a few ways in which lead batteries age, anodic corrosion, sludging, shedding, sulfation to name a few. This means that the old an new batteries will not be charged at the same level. The new batteries work harder than the old which ages them quicker.
 

xNYCMarc

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I'm going to have to disagree, at least as far as lead batteries are concerned. I've played mix and match many times over the years and have seen many others do it as well. There is no doubt in my experience that mixing old and new batteries will result in a shorter over all lifetime. When I started off grid decades ago, I used all kinds of used batteries, played with de-sulfaters, you name it. I have seen first hand many times the effect of adding beat up batteries to new batteries. I won't say it destroys them but shortens life span for sure. How much effect it has depends on how beat the old batteries are. As lead batteries age their internal resistance goes up and the charge capacity goes down. There are quite a few ways in which lead batteries age, anodic corrosion, sludging, shedding, sulfation to name a few. This means that the old an new batteries will not be charged at the same level. The new batteries work harder than the old which ages them quicker.
How do you know it was "a shorter life overall" when you played mix and match if you don't run a "control" at the same time that isn't mixed with old and new batteries? That is not science. You FEEL like something should have lasted longer, but you don't actually know if it was "normal" or not. I've ACTALLY done these experiments myself so I would know first hand. Parallel mixing of slightly different amp-hour capacities has ABSOLUTELY ZERO shortening effect on cells. In FACT, it increases the life of a cell beyond what it would have been if you were pulling the same power through the cell by itself. The "load" is shared between the multiple cells instead of a single cell taking all of the load. Even if you took seriously old beaten down cells, the amp draw on the "old" one would be nearly nill. The "new" cell would be doing almost all the work and it would be almost as though the "old" one wasn't even there since it's basically doing nothing.
 

boondox

Chief Engineer, RedNeckTech Industries
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Messages
655
Well, tell that to the battery manufactures. Ask them if they will honor their warranty if you mix old cells with new. You mention mixing batteries of different amp hour capacities above and that is not what we are discussing here.

I assume then in your tests you have done proper controls over many years? If so I would be most interested in reading your white papers on the subject. And I would admit that I certainly have not done tests with proper controls. However that doesn't change the fact that much practical experience has shown me it to be true. And the industry agrees.

Oh, and putting some words in all caps doesn't actually strengthen your arguments.
 

Wellbuilt

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637
Hmmmm , Marc you are wrong 😑
if you mix old and new lead acid battery’s what happens is the battery charger averages voltage when charging
so one battery get over charged a little the other battery get under charged and over time .
The over all SG gets dragged down
I’ve seen plenty of guys try to change out week battery’s in there golf carts the new battery just die in short order .
This has nothing to do with Lith battery’s they bo not apply to this
 

chrisski

Photon Sorcerer
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Aug 14, 2020
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How do you know it was "a shorter life overall" when you played mix and match if you don't run a "control" at the same time that isn't mixed with old and new batteries?
If you disagree with this so much, do you have evidence to say otherwise? I've mixed old and new batteries in parallel with dual battery diesel engines, but I have no hard data. If I said it lasted longer or didn't would be hersay.

Some things I'm not willing to spend my money on. I spent $1000 to have four solar golfcart sized, 6 volt Trojan's delivered to my house. That's a whole lot more than I paid for my tiny diesel engine batteries.
 

xNYCMarc

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Well, tell that to the battery manufactures. Ask them if they will honor their warranty if you mix old cells with new. You mention mixing batteries of different amp hour capacities above and that is not what we are discussing here.

I assume then in your tests you have done proper controls over many years? If so I would be most interested in reading your white papers on the subject. And I would admit that I certainly have not done tests with proper controls. However that doesn't change the fact that much practical experience has shown me it to be true. And the industry agrees.

Oh, and putting some words in all caps doesn't actually strengthen your arguments.
I don't need to tell it to anyone. The battery manufacturers already know this and NONE of them disagree with my findings. If you think they do, then post their findings.
Oh, and putting a word in caps isn't supposed to "strengthen my argument". It's meant to EMPHASIZE a particular word. Your misunderstanding isn't a failure on my end, it's on your end.
 

xNYCMarc

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May 4, 2021
Messages
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Hmmmm , Marc you are wrong 😑
if you mix old and new lead acid battery’s what happens is the battery charger averages voltage when charging
so one battery get over charged a little the other battery get under charged and over time .
The over all SG gets dragged down
I’ve seen plenty of guys try to change out week battery’s in there golf carts the new battery just die in short order .
This has nothing to do with Lith battery’s they bo not apply to this
This is IMPOSSIBLE in parallel. What you are describing is what happens in series.
 

xNYCMarc

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Messages
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If you disagree with this so much, do you have evidence to say otherwise? I've mixed old and new batteries in parallel with dual battery diesel engines, but I have no hard data. If I said it lasted longer or didn't would be hersay.

Some things I'm not willing to spend my money on. I spent $1000 to have four solar golfcart sized, 6 volt Trojan's delivered to my house. That's a whole lot more than I paid for my tiny diesel engine batteries.
Hearsay is exactly what I'm talking about. Until someone does an experiment with a proper control, like I have, then they are guessing. I understand if you don't want to spend your money on something. But I wanted to know for sure for myself. So I did it and I guess it was lucky for me tha it ended up not being a waste of money. But I was willing to waste it in exchange for learning something.
 

Wellbuilt

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Parrelling even new lead acid battery’s will kill them quick , it is common knowledge that you should not use more then 3 parallel battery’s ?
 

boondox

Chief Engineer, RedNeckTech Industries
Joined
Mar 1, 2020
Messages
655
I really doubt the juice is worth the squeeze here but...

While I agree that mixing lead batteries of different ages in series is more problematic, there are issues with parallel too. The older batteries having a higher resistance will not work as hard. The new batteries will make up the difference. After the sun goes down all batteries will attempt to equalize themselves. The old batteries are not capable of reaching as high a charge as the new batteries but the new batteries will try to get them there. Therefore all of the batteries wind up in a lower state of charge. Which leads to sulfation and other issues.

You like to say that you have done the research, so let's see it. Make sure to show it to the big lead battery manufacturers as well, their research clearly was not as well done as yours. After all, they have only been making lead batteries for over 100 years so they have much to learn I am sure.
 
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