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Extending a part worn battery bank

Well, of course in at least one sense almost all batteries are in series, except for 1.5 volt cells. What I have seen cause issues however is 6 volt batteries in series/parallel to form large 12 volt banks. In general when one 6V battery goes bad the other in series will quickly follow. I have replaced one (really quick problems) and both in the string. In either case, in short order the battery will not charge above what the others in the array are, as measured with a hydrometer. Removing the batteries from the bank and charging them separately they still would not charge fully. Even an EQ charge won't remedy it. So they had been degraded by being in parallel with the other batteries. Remember, this happened when both batteries in series were replaced. I have seen the same thing when 12V batteries were used to form the bank.


I very much agree that inserting a new battery in series with old ones is a quick recipe for trouble. But parallel use will too, just not as drastically as series. I have seen this on multiple occasions back in the day when we all ran large banks of 6V FLAs to form large banks of 12V. Back then 12V inverters were all that was available and the banks were very large parallel arrays. I admit the data is fuzzy because there are other factors at play. Asymmetrical connections, unequal cable lengths, some connections not as good as others are all influencing pack aging. Nonetheless, I have seen batteries sink to the lowest common denominator within a couple of months and be unable to charge fully. Even within a couple of weeks they will read the same as the rest of the bank but will still fully charge if taken out of the bank. I have been living on FLAs for over 20 years and have helped many people with their off grid systems and have worked with many battery banks.


And really, do call Crown or Surrette. I guarantee they will tell you it is not a good idea. None of the reputable solar installers I know recommend replacing weak cells with new ones. Personally my rule of thumb is put a load test on the used but good batteries and if they test above 80% it is worth it to put a new battery in it. If not, just lower the cut out voltage if needed and keep beating on the bank until it is dead, then replace the entire thing.
" In general when one 6V battery goes bad the other in series will quickly follow."
I would agree. That happens because the cells were all operated under the same conditions for exactly the same length of time. They all got old together. I fly airplanes and the same thing happens to the light bulbs on the plane. If the right side "nav light" burns out and I only change that bulb, a few days later the left "nav light" burns out, then 3 days later the rear one burns out. That happens because all the nav-lights are on at the same time and they run for the same length of time. So I just change all of them when one burns out since the others aren't far behind. BUT I must point out that you are talking about batteries in SERIES, which we were already on the same page about that it can't be done with series cells. If you have multiple strings of cells, you run into the same problem of the batteries all getting old at the same time since they are in use at the same time for the same length of time, thus multiple strings can go bad at almost the same time for that same reason.
 
No, it is parallel that causes the issue. Yes, there are two batteries in series. But even replacing both still results in degradation. The same would happen with a 12v battery in parallel. It isn't the same as your light bulb analogy. It isn't that the batteries all get old at the same time. The new battery reads the same as the old batteries in a period of a month or two. It has lost the same amount of capacity as the batteries that are several years old. So a more rapid than usual loss of capacity has taken place and it is measurable with a hydrometer and a load tester. It is nothing like your light bulb analogy, that would be like you replaced on bulb and then it and all the others burned out one after the other. The older batteries continue functioning as they were. It is only the new battery that loses capacity.
 
No, it is parallel that causes the issue. Yes, there are two batteries in series. But even replacing both still results in degradation. The same would happen with a 12v battery in parallel. It isn't the same as your light bulb analogy. It isn't that the batteries all get old at the same time. The new battery reads the same as the old batteries in a period of a month or two. It has lost the same amount of capacity as the batteries that are several years old. So a more rapid than usual loss of capacity has taken place and it is measurable with a hydrometer and a load tester. It is nothing like your light bulb analogy, that would be like you replaced on bulb and then it and all the others burned out one after the other. The older batteries continue functioning as they were. It is only the new battery that loses capacity.
If you believe that the parallel causes the issue, then you're free to continue believing that. I get no benefit by changing your mind. I don't sell battery systems or do install services or anything like that. So I will leave it at that.
 
None of the claims mean anything without at the very least a link to a paper explaining it.

I don't care what qualifications anyone has, if you can't provide the data or at least demonstrate the math behind it then your claim can't be trusted with certainty.

This argument is going in circles with zero productivity.

The simple fact is that op CAN mix batteries (nothing physically stopping it) and MAY see decreased life. Whether that is 6 months or 6 years less remains to be seen.


My recommendation to the op is to do it anyways, assume the worst case, and consider saving up for lithium for the next time.
 
https://batteryguy.com/kb/knowledge-base/connecting-batteries-in-parallel/ (Note the bottom of the page where it says

"Connecting batteries of different amp hour capacities in parallel"​

By the way, I'm not just a "redneck engineer". I'm an ACTUAL engineer.

I went to your link and found the authors concluding remarks. They are shown in RED below. So you have referenced a source where you draw the opposite conclusion of that of the author and you have submitted this as evidence of your conclusion? There must be several nuances in your assumption like the statement below in green.

Connecting batteries of different amp hour capacities in parallel​

This is possible and won’t cause any major issues, but it is important to note some potential issues:

  • Check your battery chemistries – Sealed Lead Acid batteries for example have different charge points than flooded lead acid units. This means that if recharging the two together, some batteries will never fully charge. The result here would be sulfation of those that never reach a full state of charge, reducing their lifespan.
  • Double check voltages – if you are using batteries with different amp hour capacities, it is highly likely that the voltages will be different (even if the stated voltage on the labels match). Check this with a voltmeter or you will experience problems (covered in connecting batteries of different voltages in parallel above).
It is for these reasons that you are advised to use batteries of the same brand, voltage and capacity. Failing to do so (if you don’t have the knowledge and tools to check what you are doing) could create a potentially dangerous circuit.

Here is another reference easily found on Google that also discourages mismatched parallel LA batteries.


I also have a couple of degrees, one says "Electrical Engineering", and the second one says "Electrical and Computer Engineering". I did not know that a UC school would award "Science degrees" from a college of engineering?
 
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Recommendations that you generally shouldn't because its less than ideal and "under no circumstances should you ever do this" are very different situations though.


Possible? Yes.

Ideal? No.

Will reduce life? Possibly, maybe probably.

It's for you as the person spending your money to decide if the drawbacks are worth it for the gain required.
 

I went to your link and found the authors concluding remarks. They are shown in RED below. So you have referenced a source where you draw the opposite conclusion of that of the author and you have submitted this as evidence of your conclusion? There must be several nuances in your assumption like the statement below in green.

Connecting batteries of different amp hour capacities in parallel​

This is possible and won’t cause any major issues, but it is important to note some potential issues:

  • Check your battery chemistries – Sealed Lead Acid batteries for example have different charge points than flooded lead acid units. This means that if recharging the two together, some batteries will never fully charge. The result here would be sulfation of those that never reach a full state of charge, reducing their lifespan.
  • Double check voltages – if you are using batteries with different amp hour capacities, it is highly likely that the voltages will be different (even if the stated voltage on the labels match). Check this with a voltmeter or you will experience problems (covered in connecting batteries of different voltages in parallel above).
It is for these reasons that you are advised to use batteries of the same brand, voltage and capacity. Failing to do so (if you don’t have the knowledge and tools to check what you are doing) could create a potentially dangerous circuit.

Here is another reference easily found on Google that also discourages mismatched parallel LA batteries.


I also have a couple of degrees, one says "Electrical Engineering", and the second one says "Electrical and Computer Engineering". I did not know that a UC school would award "Science degrees" from a college of engineering?
How do I draw the opposite conclusions to that of the author? It says in green "This is possible and won’t cause any major issues".
The part in red is the "cover my ass" statement that "if you don't know what you're doing, it could be a problem. But knowing what you're doing shouldn't be a problem since there is nothing inherently wrong with it.

" I did not know that a UC school would award "Science degrees" from a college of engineering?"


Berkeley Engineering is a national leader in engineering education, with students and researchers from around the world drawn to our department by its outstanding reputation, internationally recognized faculty, and tradition of impact in research and teaching. The College includes departments of Bioengineering; Civil & Environmental Engineering; Electrical Engineering & Computer Sciences; Industrial Engineering & Operations Research; Materials Science & Engineering; Mechanical Engineering; and Nuclear Engineering.

The Management, Entrepreneurship, & Technology (M.E.T.) Program is a new program for students interested in a major from both the College of Engineering and the Haas School of Business.

Majors​

  • Aerospace Engineering
  • Bioengineering
  • Civil Engineering
  • Electrical Engineering and Computer Science
  • Engineering Science Programs
    • Energy Engineering
    • Engineering Mathematics and Statistics
    • Engineering Physics
    • Environmental Engineering Science
  • Industrial Engineering and Operations Research
  • Materials Science and Engineering
  • Mechanical Engineering
  • Nuclear Engineering
  • Management, Entrepreneurship, and Technology (M.E.T.)*
    • Bioengineering & Business Administration
    • Civil Engineering & Business Administration
    • Electrical Engineering and Computer Science & Business Administration
    • Industrial Engineering and Operations Research & Business Administration
    • Materials Science and Engineering & Business Administration
    • Mechanical Engineering & Business Administration
    • Undeclared Engineering & Business Administration
  • Mills 3+2 Engineering Program*
  • Undeclared Engineering*
 
How do I draw the opposite conclusions to that of the author? It says in green "This is possible and won’t cause any major issues".
The part in red is the "cover my ass" statement that "if you don't know what you're doing, it could be a problem. But knowing what you're doing shouldn't be a problem since there is nothing inherently wrong with it.

" I did not know that a UC school would award "Science degrees" from a college of engineering?"


Berkeley Engineering is a national leader in engineering education, with students and researchers from around the world drawn to our department by its outstanding reputation, internationally recognized faculty, and tradition of impact in research and teaching. The College includes departments of Bioengineering; Civil & Environmental Engineering; Electrical Engineering & Computer Sciences; Industrial Engineering & Operations Research; Materials Science & Engineering; Mechanical Engineering; and Nuclear Engineering.

The Management, Entrepreneurship, & Technology (M.E.T.) Program is a new program for students interested in a major from both the College of Engineering and the Haas School of Business.

Majors​

  • Aerospace Engineering
  • Bioengineering
  • Civil Engineering
  • Electrical Engineering and Computer Science
  • Engineering Science Programs
    • Energy Engineering
    • Engineering Mathematics and Statistics
    • Engineering Physics
    • Environmental Engineering Science
  • Industrial Engineering and Operations Research
  • Materials Science and Engineering
  • Mechanical Engineering
  • Nuclear Engineering
  • Management, Entrepreneurship, and Technology (M.E.T.)*
    • Bioengineering & Business Administration
    • Civil Engineering & Business Administration
    • Electrical Engineering and Computer Science & Business Administration
    • Industrial Engineering and Operations Research & Business Administration
    • Materials Science and Engineering & Business Administration
    • Mechanical Engineering & Business Administration
    • Undeclared Engineering & Business Administration
  • Mills 3+2 Engineering Program*
  • Undeclared Engineering*
So which is your degree? I'm still curious
  • Engineering Science Programs
    • Energy Engineering
    • Engineering Mathematics and Statistics
    • Engineering Physics
    • Environmental Engineering Science
 
So which is your degree? I'm still curious
  • Engineering Science Programs
    • Energy Engineering
    • Engineering Mathematics and Statistics
    • Engineering Physics
    • Environmental Engineering Science
Why? You're already questioning it's existence to the point where you tried to insinuate that the school doesn't even have a science program. I tune people like that out. If you disagree with my findings about the batteries, that's fine. But don't attack my education.
 
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Why? You're already questioning it's existence to the point where you tried to insinuate that the school doesn't even have a science program. I tune people like that out. If you disagree with my findings about the batteries, that's fine. But don't attack my education.
I think you are hyper-sensitive, I did not attack your degree but rather just asked what I was it because the degree doesn't seem to specify that.
 
I think you are hyper-sensitive, I did not attack your degree but rather just asked what I was it because the degree doesn't seem to specify that.
I would add too that a general mech E degree doesn't specialize in anything and means nothing about qualifications in a given field without years of work experience related to it.

Anyone with an education should understand this already.

You come out with enough knowledge to pick a field and start learning, but are not an expert on anything they teach, even if you specialized, until a masters level at minimum and most of them will agree by that point that they still have much I learn.

So like in my case I'm in plastic injection molding.

I know a bit about designing and specifying equipment, sizing electrical/pnuematic/hydraulic/heat loads and storage capacity, heat transfer, turbulent flow, non-newtonian fluids, and most of all plastic injection processing....

But I am by no means an expert at anything other than the actual melt processing (and I'd be a fool to claim I'm the authority on the matter), despite my generalized education on all of those things.

When I need an expert, I call one who gets paid very well to be that expert.


Somewhat back to the point, even an EE would be much better suited for the discussion but it's quite possible that an accomplished electrical engineer may even have zero experience on this exact specific topic of batteries.

So even further to the point, it's not exactly an invalid question to ask if one is specialized in the field of energy storage because "engineering degree", while a respectable accomplishment of course, does not mean much in its own right when it comes to a specific topic.

As before, I know a little about a lot of things. But I'm not an expert on 99% of the things I've dabbled in.

And at the end of the day nobody is posting anything technical enough to warrant this stupid debate about education in the first place. What has been posted is little more than an opinion piece, followed up by opinions, and a whole bunch of chest beating about how that opinion is better.
 
I have two sets of L-16 large format batteries, one Rolls Surette S-530 L-16 400 a.h. Solar duty deep cycle and one set Interstate (rebadged US Battery) L-16 426 a.h. floor sweeper duty, they do not like to be in parallel period...one will be too low s.g. and the other will boil.

Rolls Surette’s lead engineer told me directly that I should keep them separate as they are NOT THE SAME ,
Interstate’s Lead foreman at the Salinas Ca. plant said the same thing

The s.g. are not the same 1.277 for the Interstate and 1.265 for the Surette’s the charge voltages are not the same 28.8 for the Interstate and 30.0 for the Surette

To that end I have two fully programmable separate charge controllers, MidNite Classic ,separate battery monitors etc. Bogart Engineering Tri-Metric These are kept totally seperated. Grounds are tied together but one bank is used at a time
Its not that I need that much capacity at a time, But I have a difficult water pump down 420 feet with a water level of -250 to -350 feet, so pretty much a big load if i'm in the coastal fog for days and cant get at least 50 amps charge

When you buy a set of Rolls Surette batteries they are made on the same day ,by the same tech, and have sequential serial numbers and shipped as a “matched set” with instructions not to attempt to “mix and match”
This system has been in use for 16-17 years now with no issues at all the Surette’s came out the door 2 26 2005, the Interstates are about 6 months older

In 1965 when I was Uniuersity of Alaska in Fairbanks Alaska I paid my way through college working at Alaska Husky Battery where we built Flooded Lead Acid Arctic batteries much thicker plates than any normal car battery with the hottest acid i have ever seen in a FLA 1.320....these were Arctic batteries to be used in the winter only. They would not survive the Arctic summer 80-90 F in Fairbanks under the hood.....way too hot for such a hot battery, just like your snow tires, keep them in the barn for the summer, save them for next winter.
When a customer need one battery for a two battery setup it was sold with a very restricted warranty as the old one will drag down the new one and it will fail prematurely....every time. finally they would not sell you one.

The US Employment Prevention Agency (EPA) ran Alaska Husky Battery out of business....for a while, they are now in Moscow, Russia making the same battery for the Russian Arctic
Deka is another very high end battery producer who insists on selling the set....same reason

Thats 4 battery manufacturers who do not recommend mixing batteries. I have never heard of any battery manufacturer who recommends mixing new with aged batteries or dissimilar types of batteries

Let me see 1965 to 2021 thats 56 years lead acid expereince that says FLA is not a mix n match.

Obviously I do not beleive a word of what someone is saying


But i dont know nada.....

29 years engineer at General Electric Corporation DC to microwave , 20 years electric contractor, 50% owner of auto repair shop, Interstate dealer (the shop, not me personally)

You cant argue with someone who knows everything, not even worth the time.....
 
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So your professional opinion is that you can do it, you generally shouldn't do it if you can help it, and that if you do so you should be prepared for long term issues?
 
Ya got it, very rarely i will be forced to parallel my sets, but I allways seperate the systems so they can recharge to their own settings.

In my shop you can not buy one battery for your 2 battery diesel truck, I do not like having to deal with the warranty issue. You need one there is kmart, cosco, but dont ask me to work on it. I only do severe electrical problems, mostly a silent partner but im the electrical wizard

I have one good case for using mismatched batteries, You are up bear creek road on the side of the mountain , its raining cats and dogs, the mud is getting deep, wind is howling and you need to get home...and that is all you have!
And oh ya, the lightning bolts are getting closer.....
 
I would add too that a general mech E degree doesn't specialize in anything and means nothing about qualifications in a given field without years of work experience related to it.

Anyone with an education should understand this already.

You come out with enough knowledge to pick a field and start learning, but are not an expert on anything they teach, even if you specialized, until a masters level at minimum and most of them will agree by that point that they still have much I learn.

So like in my case I'm in plastic injection molding.

I know a bit about designing and specifying equipment, sizing electrical/pnuematic/hydraulic/heat loads and storage capacity, heat transfer, turbulent flow, non-newtonian fluids, and most of all plastic injection processing....

But I am by no means an expert at anything other than the actual melt processing (and I'd be a fool to claim I'm the authority on the matter), despite my generalized education on all of those things.

When I need an expert, I call one who gets paid very well to be that expert.


Somewhat back to the point, even an EE would be much better suited for the discussion but it's quite possible that an accomplished electrical engineer may even have zero experience on this exact specific topic of batteries.

So even further to the point, it's not exactly an invalid question to ask if one is specialized in the field of energy storage because "engineering degree", while a respectable accomplishment of course, does not mean much in its own right when it comes to a specific topic.

As before, I know a little about a lot of things. But I'm not an expert on 99% of the things I've dabbled in.

And at the end of the day nobody is posting anything technical enough to warrant this stupid debate about education in the first place. What has been posted is little more than an opinion piece, followed up by opinions, and a whole bunch of chest beating about how that opinion is better.
The thing is that the question of "Which degree do you have so we can determine what your expertise is" wasn't asked. What was said and implied was "hey, your school doesn't even offer the program that you supposedly earned a degree in", which if true would be a "gotcha" moment that I wasn't authentic. But it was said without even doing a basic check to see if it was even true, which I showed obviously wasn't true. That's what I have a problem with.
 
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