Extending a part worn battery bank

Texas-Mark

Solar Addict
Joined
Aug 4, 2021
Messages
495
Fascinating. Can you tell us more about your batteries, type, configuration, how it is used and so on?

Small 12V system with 1500W solar, I have 5 FLA and 4 AGM batteries in parallel. This is primarily used to run a pool pump but also to run a 10K BTU air conditioner in my shop occasionally. Yes the mixing of FLA and AGM batteries is another thing some people say not to do, but yet It has been working fine for me. I can test the SG of the FLAs easily enough, but the AGMs I just put a load tester on once every 6 months so. As long as everything keeps working (and it has), I don't worry about it. My current FLAs are between 2 and 6 years old. When the oldest one gives it up, I will just replace it.

IMO proper maintenance is the key, along with not over-discharging.

<edit> Stupid auto correct
 
Last edited:

Samsonite801

Solar Addict
Joined
Oct 15, 2020
Messages
870
Here's a thought...

Wait til Black Friday, buy a set of new batteries at half-price so you don't care what happens to them and then mix old with new without a care. Or if you got them at half price on Black Friday, you could maybe afford to just buy the whole new set and decomm the old batteries (or use them in another application like a solar street light or a tractor, jumpstart battery or something)...

Did you already do an equalize on your old lead batteries to see if you could clean the plates off a bit and get back some of the capacity? I did install a 'Pulsetech PowerPulse Battery Maintenance System' on a few batteries I've owned (with success) and they seemed to clean the plates off enough to get capacity back.

Or could check with a battery re-manufacturer to see if you could just buy some used batteries that are a good match with your current set... When I was young we had a place near us called Beacon Battery where I could go get used AGM or Gel batteries for $16 each (were take-outs from the cable companies comm equipment), and I still have one of those gel ones from 20+ years ago and it still works today... knock on wood...
 
Last edited:

boondox

Chief Engineer, RedNeckTech Industries
Joined
Mar 1, 2020
Messages
655
Small 12V system with 1500W solar, I have 5 FLA and 4 AGM batteries in parallel. This is primarily used to run a pool pump but also to run a 10K BTU air conditioner in my shop occasionally. Yes the mixing of FLA and AGM batteries is another thing some people say not to do, but yet It has been working fine for me. I can test the SG of the FLAs easily enough, but the AGMs I just put a load tester on once every 6 months so. As long as everything keeps working (and it has), I don't worry about it. My current FLAs are between 2 and 6 years old. When the oldest one gives it up, I will just replace it.

IMO proper maintenance is the key, along with not over-discharging.

<edit> Stupid auto correct

Interesting. You have two theoretical no-no's there and yet it's working What sort of overnight discharge do you see? What is the wH of the bank and how much typically gets pulled out over night? I'm trying to think of any other factors that might make the difference between our observations.
 

Texas-Mark

Solar Addict
Joined
Aug 4, 2021
Messages
495
Interesting. You have two theoretical no-no's there and yet it's working What sort of overnight discharge do you see? What is the wH of the bank and how much typically gets pulled out over night? I'm trying to think of any other factors that might make the difference between our observations.

I have a 1200 Ah bank. I typically pull around 200Ah during the night. On sunny days, I am back to 100% by 1 or 2 pm. I have a very conservative low battery cutoff with a 24 hour time delay before things will switch back on. That helps prevent keeping the batteries from hovering around that cutoff voltage.

Not directed at you, but I often see things posted that people say won't work, but yet they never actually tried it. On another forum (not solar related) there was a machining issue that for years people said would not work for this reason or that. Then one day someone just did it and it worked just fine. All you heard after that was crickets from the naysayers.

There is another thread here where several people have posted that they have mixed FLA and LiFePo4 batteries without issue despite the same "theories" that it would not work or should not be done.

Is it possible I am shortening the life of the newer batteries? Sure. But by how much? If I am loosing 6 months off of one, it is still way cheaper to replace one a bit early, than replacing the whole bank just because one battery crapped out.
 

boondox

Chief Engineer, RedNeckTech Industries
Joined
Mar 1, 2020
Messages
655
I have a 1200 Ah bank. I typically pull around 200Ah during the night. On sunny days, I am back to 100% by 1 or 2 pm. I have a very conservative low battery cutoff with a 24 hour time delay before things will switch back on. That helps prevent keeping the batteries from hovering around that cutoff voltage.

Not directed at you, but I often see things posted that people say won't work, but yet they never actually tried it. On another forum (not solar related) there was a machining issue that for years people said would not work for this reason or that. Then one day someone just did it and it worked just fine. All you heard after that was crickets from the naysayers.

There is another thread here where several people have posted that they have mixed FLA and LiFePo4 batteries without issue despite the same "theories" that it would not work or should not be done.

Is it possible I am shortening the life of the newer batteries? Sure. But by how much? If I am loosing 6 months off of one, it is still way cheaper to replace one a bit early, than replacing the whole bank just because one battery crapped out.

Oh, no offense taken here at all. I don't know if you have read through the entire thread but I have taken S.G. measurements in various scenarios and have found measurable loss of capacity. In one of my examples above with the new battery bank I got last year, some of the batteries I got wouldn't charge above 90%. Four of the batteries would charge to 100%. Within a month or so the hot batteries were down to being able to charge to 90%. When I have mixed batteries that were pretty beat I have seen a more drastic loss of capacity. While 10% isn't a big deal in one way, losing 10% of the top of a new bank didn't make me happy.

I'm not married to any particular "truth". I am just curious. I believe my measurements and I have no reason to doubt yours. So I am just digging to see what comes to light.
 

Texas-Mark

Solar Addict
Joined
Aug 4, 2021
Messages
495
some of the batteries I got wouldn't charge above 90%

How are you calculating that they won't charge above 90%? If using specific gravity, what are you using to measure it? I used to use one of those "turkey baster" floats, but found them to be horribly inconsistent. Now I use a refractometer and find it to be way more consistent. Also, I run an equalization charge on the FLAs every couple months using an external charger. That always seems to perk up any that are laggy.

Perhaps I don't have issues because I don't run my bank very hard. With 9 batteries, I am not draining them very much each day.
 

boondox

Chief Engineer, RedNeckTech Industries
Joined
Mar 1, 2020
Messages
655
How are you calculating that they won't charge above 90%? If using specific gravity, what are you using to measure it? I used to use one of those "turkey baster" floats, but found them to be horribly inconsistent. Now I use a refractometer and find it to be way more consistent. Also, I run an equalization charge on the FLAs every couple months using an external charger. That always seems to perk up any that are laggy.

Perhaps I don't have issues because I don't run my bank very hard. With 9 batteries, I am not draining them very much each day.

In the past it was a hydrometer only. Now I have a refractometer too but I find it tracks with my hydrometer pretty well, which is one of the E-Z-RED temperature compensated jobs. The do have a slight difference of opinion as to the absolute numbers but the relative numbers are spot on. Meaning if one measures .05 difference the other does too but the refractometer reads .02 or something higher than the hydrometer. I actually bought the refractometer to make sure that my hydrometer was reading right when I got the batteries in the example we are discussing. It's handy for coolant too.
 

Wellbuilt

Solar Addict
Joined
Sep 14, 2020
Messages
637
It impossible to get to full charge if one battery gets filled up first .
The charger sees the Average of all the batteries involved whether it’s a series or parallel .
And lead acid battery need to reach full charge every day or so .
I’ve seen people lose a battery bank in 2 months of poor charging .
New and old battery’s have different charging requirements sooooo one is getting over charged (boiling)
the others is being under charged ( losing capacity) it’s just what happens .

the bank I have in my trailer is 2 GC 215 ah battery’s they just finished there 6 season
The first year they needed very little water and would be charged after 11/2 hour absorb .
6 years later they absorb for 5 hour and will still get charged but not to the same level and it takes hours longer .
Now how could mixing them work ?
I’ve tried adding one or 2 battery’s to a bank , And they died with in one season .
The only luck I’ve ever had was replacing a old worn out battery with a old battery that was still
Serviceable of same type and approximate age .
Sams club sells a ton of battery’s 6 or8 at a time and get the cores back it’s easy to find good battery’s in the bunch.
It’s hard enough to keep all the same battery’s charged and happy as it is .
You may be doing ok because you are not using a lot of power 🤷‍♂️
But my bank will start to drift buy the end of January if it dosent get full charge every few day or if I start dropping my battery 35% before charging .
 

Texas-Mark

Solar Addict
Joined
Aug 4, 2021
Messages
495
It impossible to get to full charge if one battery gets filled up first .
The charger sees the Average of all the batteries involved whether it’s a series or parallel .
And lead acid battery need to reach full charge every day or so .
I’ve seen people lose a battery bank in 2 months of poor charging .
New and old battery’s have different charging requirements sooooo one is getting over charged (boiling)
the others is being under charged ( losing capacity) it’s just what happens .

I disagree. When in parallel, the "full" one will taper off it's charge current while the other ones continue to charge (over-simplification)

Sorry, but none of my batteries are boiling, and as I said, this process (different age batteries) has been working fine for a decade. <shrug>
 

boondox

Chief Engineer, RedNeckTech Industries
Joined
Mar 1, 2020
Messages
655
My observations with FLA is consistent with what @Wellbuilt is saying in terms of boiling. While boiling might be too strong a word, when measuring the SG of the old and new batteries I have seen more bubbles in the older battery. @Texas-Mark , I wonder if maybe your selaed batteries are the ones reaching charge first? Or what other factors we may not be considering?
 

Texas-Mark

Solar Addict
Joined
Aug 4, 2021
Messages
495
I wonder if maybe your selaed batteries are the ones reaching charge first? Or what other factors we may not be considering?

Hard to tell with those since they are sealed. But they are about 4 1/2 years old and still ticking.

As for other factors, I keep my charge voltage somewhat lower at 14.1V (it is also temperature compensated via a BTS). When I monitor the charge current, it tapers off just as I would expect it to (in relation to the capacity meter getting to 100%). Note: the capacity meter is separate from the charge controller. The only time I have observed any bubbling is when I intentionally do an equalization.

But again, I think a lot has to do with good battery maintenance. I don't have any abused batteries in the bank.
 

Wellbuilt

Solar Addict
Joined
Sep 14, 2020
Messages
637
The only thing i can think of , is if you shallow cycle the battery’s it my not affect them as much.
Cold would could allso prevent them from getting hot but it allso slows charging and allso slows
build up of crystels on the plates .
But if it dosent matter if if the battery’s are all at a diffrent rate of charge why bother EQing them at all ?
It’s got to be better to just follow battery manufacturers recommendations .
there is a guy that lives on the next mountaintop that has sams GC battery’s going on 12 years and he uses them in his garage now for lites and radio he has e8in series 3 in parallel for 24 total .
I like the description boiling the battery’s are also hot .
14.1 is really low for any type of lead acid battery? Really low
gell cells get 14.4 volt and its customary for LA battery’s to get 14.7 14.8 v
 

Texas-Mark

Solar Addict
Joined
Aug 4, 2021
Messages
495
Cold would could allso prevent them from getting hot but it allso slows charging and allso slows
build up of crystels on the plates .
But if it dosent matter if if the battery’s are all at a diffrent rate of charge why bother EQing them at all ?


I'm in Texas LOL
I have always equalized FLA batteries that are stationary for extended periods.
I keep the charge voltage lower because it does get hot here (BTS or not).
I think they would be boiling at 14.7v to 14.8v

In any case, all I can say is it has been working. The only time I had "matched" batteries is when I first built the system about a decade ago.
 
Last edited:

Tecnodave

Solar Addict
Joined
Mar 22, 2021
Messages
519
If you are getting 10 years on golf cart batteries you are doing something right, my L-16 ‘s are 16 and 17 y.o. and still going strong, I do not get anything like that with the telco AGM batteries that i use in other systems but those were not designed for daily cycling. They are 3-4 y.o. when i get them free from the telco. But i do get a few good years out of the ones that pass the first tests.
 

Texas-Mark

Solar Addict
Joined
Aug 4, 2021
Messages
495
If you are getting 10 years on golf cart batteries you are doing something right,

These are not golf cart batteries. They are off the shelf marine batteries. I did not say I have gotten 10 years out of them, I said I have been just changing out batteries as needed for the last 10 years. But overall I am only on my second set. I just checked the SG on them and they are all in the "green". The highest reading one is 4 years old. <shrug> The oldest battery is about 5 1/2 years and the newest one is about 1 1/2 years old (hence the 4 year spread).

I initially started with 3, then added another one after about a year, and then another one about a year later. That started the cycle of not having them all the same age.

Sort of off topic, but I have considered switching to LiFePO4, but I just can't justify it when I only have to swap out one $100 battery every one or two years. I probably will not be alive for 8,000 cycles, LOL
 

xNYCMarc

Solar Enthusiast
Joined
May 4, 2021
Messages
36
Small 12V system with 1500W solar, I have 5 FLA and 4 AGM batteries in parallel. This is primarily used to run a pool pump but also to run a 10K BTU air conditioner in my shop occasionally. Yes the mixing of FLA and AGM batteries is another thing some people say not to do, but yet It has been working fine for me. I can test the SG of the FLAs easily enough, but the AGMs I just put a load tester on once every 6 months so. As long as everything keeps working (and it has), I don't worry about it. My current FLAs are between 2 and 6 years old. When the oldest one gives it up, I will just replace it.

IMO proper maintenance is the key, along with not over-discharging.

<edit> Stupid auto correct
I'm glad to see that someone has experienced in real world usage what my experiments found to be true.
 
Top