How to Store Batteries Long Term (or, should/could I make a larger battery bank)?

[JBK]

Hope this is a good place to post this.


I got a windfall today, and am not sure what to do with it...

A few weeks ago I bought 4 Interstate "Extreme" 6V batteries. What were delivered to the authorized dealer were 4 Interstate "Heavy Duty" 6V batteries.

No big deal. A week later they call for me to pick up the correct batteries; so I do, and take them home.

While installing them I noticed that the new "Extreme" batteries had the same scuff marks (the sort that happen during shipping) as the "Heavy Duty" ones that were returned.

I called the main Interstate office, and they did a bit of cross referencing of the manufacturing number etched onto the battery cases, and found that someone, instead of delivering the correct batteries, simply swapped the labels, thinking that I'd never notice.

The correct batteries are now being delivered, and I can keep the mislabeled ones. There's nothing wrong with the "Heavy Duty" batteries; just wasn't what I paid for.

So to my question.

I now have 4 "Heavy Duty" and 4 "Extreme" batteries. Can I use all 8 to expand my current 4-battery battery bank setup, bearing in mind the half the batteries are slightly different from the other half?

Or, considering that my current 4-battery setup works just fine, the batteries will eventually die, and new batteries are beyond our means (I had to borrow money for these), is there a way to store 4 of them for back-up (for several years)? How long could the back up batteries be expected to last (near new condition, and separately, usable condition) on a shelf, with periodic maintenance?

 

[Mark_K5LXP]

Swapping the labels? Man, talk about zero ethics and integrity. Reminds me of a joke about a blue suit.

Are these the same Ah rating? I don't know these batteries specifically but in some cases the same batteries are marketed under a different moniker, with the only difference being the cost and warranty period. If they're the same, then check the box, you doubled your capacity. If not but the Ah ratings are the same, this could work for a "while", meaning some period of calendar time and cycles. As the batteries are used and as they age, if they are truly different structurally, they will likely start to diverge and the weaker ones will become more apparent. If you can get a datasheet for each one (good luck with that with Interstate) you can decide if a mixed bank is conceivable, or should be avoided at the outset.

There is no practical way to store lead acid batteries. Sitting idle even on a float charger they're degrading and while an older set maintained this way will be "better" than ones that were in regular service for the same period, their cycle life and performance will be ever diminishing with time.

If it's decided you don't want to mix two types in a bank my vote would be to offer them for sale. You won't get new price but since they were "free" you could readily recoup a useful value for your time and trouble for this venture.

Mark B.
Albuquerque, NM

 

[JBK]

The "Extreme" are rated as 225 Amp Hours (AH)@20 Hr.

"Heavy Duty" are rated as 210 Amp Hours (AH)@20 Hr.

As an aside, what does the "@20 Hr" part of the rating mean? I copied and pasted the rating from their site.

 

[JBK]

Also not sure, if I decide to sell them, how to explain that contrary to the "Extreme" label (that was switched) they are perfectly good "Heavy Duty" batteries.

 

[Mark_K5LXP]

what does the "@20 Hr" part of the rating mean

It's the rate at which the current is drawn from the batteries. The standard for the Ah rating of lead acid storage batteries is the current over a period of 20 hours. So for an example 220Ah battery, 220Ah's is the cumulative of 11 amps for 20 hours. First order observation would be then why couldn't you say 22 amps for 10 hours or 220 amps for 1 hour? Because, due to primarily electrolyte diffusion as currents increase, gradients across the grids and plates along with some ohmic losses, you get fewer amp hours out of the battery the faster you try to draw it out. "Better" batteries (e.g Trojan) will specify their delivered power at rates other than C/20 (C/10, C/5 and 75A rates). But C/20 is the standard and it offers a means of more or less direct comparison from one battery to another.

how to explain that contrary to the "Extreme" label (that was switched) they are perfectly good "Heavy Duty" batteries.

So remove them. What isn't there doesn't need to be explained. Maybe you can source a photo, flyer, brochure or data sheet that documents their provenance in some way like the date code scheme, case color/style, molded marks, etc. If you're not offering them as "new" then they're "as-is" and not having labels is part of the deal. You can simply state you received the wrong ones and that's a perfectly truthful statement.

Mark B.
Albuquerque, NM

 

[JBK]

So, with the batteries being the same in all ways, as far as any Interstate site documentation claims, except for the Ah, could they be used together in the same bank? Should they? If so, should I assume that I would be getting the lesser Ah across all of them?

 

[Gary RV_Wizard]

So, with the batteries being the same in all ways, as far as any Interstate site documentation claims, except for the Ah, could they be used together in the same bank? Should they? If so, should I assume that I would be getting the lesser Ah across all of them?

Yes they can be used together. Mixing different AH-rated batteries in one bank isn't theoretically ideal, but in my opinion the modest 15 AH difference between those two isn't enough to warrant any practical concerns. Especially since both are brand new. The performance characteristics will be essentially identical across a wide range of usage.

 

[Mark_K5LXP]

It's not a binary choice, the net result will depend on how the batteries are used. The more current that is drawn and restored, and the more times you do it the quicker the divergence the batteries show will happen. Gary's right, "generally" it will work OK because "most" users have neither high draws nor frequent cycling so the disparity of capacity will not be the long pole in the lifespan tent. Say, a golf cart that might see a hundred amps drawn repeatedly and daily cycling would show issues before a dozen or two amps peak for 20 days a year camping. Like an RV tire most RV batteries are more likely to age out or die of trauma than be exercised to the point their capacity difference causing accelerated demise. Is this part of an off-grid stationary bank? In that case you could make an argument to have two separate banks and switch between them to mitigate partial state of charge issues (which FLA does not tolerate particularly well).

Mark B.
Albuquerque, NM

 

[JBK]

Off grid. All we use is for LED camper lights, a Surflo water pump, an inverter for a phone and router, and the spark to start our propane fridge and water heater. No TV, no foot massagers, no disco balls

Just to make sure I got this right, our current setup has four 6V batteries, wired in series and parallel, giving us a 12V system with 210 Ah x 2 = 420 Ah. (?) So adding the other four batteries should be doubling that (420 Ah x 2 = 840 Ah)? Meaning drastically reducing the gas I have to use for the genny on cloudy days?

 

[Mark_K5LXP]

Solar helps because you stand a chance of restoring 100% but there's a strategy of using two battery banks and switching back and forth to minimize the issue of partial state of charge damage (PSOC). Maybe do some research on that and see if it would make sense for your operating scenario. The general theme is that even though you just use half the bank (and subsequent deeper draws) you extend the service life of both banks because if they were simply paralleled, PSOC would cause them to fail sooner. Practically speaking you still have the use of both, say for that cloudy day you just switch to bank 2 and when you can, the genset/solar fills them both back up so it's not like you're "stuck" with half a set. Sounds like your loads are modest, so depending on your daily Ah draw and panel size/recovery time the switched bank may not be worth the trouble. You just need to run the numbers and see.

Mark B.
Albuquerque, NM

 

[John From Detroit]

The "Extreme" are rated as 225 Amp Hours (AH)@20 Hr.

"Heavy Duty" are rated as 210 Amp Hours (AH)@20 Hr.

As an aside, what does the "@20 Hr" part of the rating mean? I copied and pasted the rating from their site.

I'd have kept the original batteries and taken a partial refund the difference in capacity is not that great. But that said... You were within your rights do demand what you ordered so I can't argue with that decision (NOTE the Refund I'd have demanded is MORE than the difference in battery price Least you think I'd be letting them get away with it)

The @20 part. For this I'm going to round down to 200 AH @20

That means if you put a controlled current load of 10 amps on the battery 20 hours later it hits ZERO .


This is kind of an industry standard... DO NOT BE FOOLED by companies that use the @1AMP METHOD THAT SAME BATTERY you might think would last 200 hours at one amp. No. closer to 250 or possibly even 300 I **THINK** I can never remember the name of the "Effect" (Starts with a P is about all I'm sure of) but this explains it

Effects of Discharge Rate and Temperature on Battery Capacity and Life

The rate at which a battery is discharged and its operating temperature have a profound effect on its capacity and life.

www.engineersedge.com

 

[RRR]

Hope this is a good place to post this.


I got a windfall today, and am not sure what to do with it...

A few weeks ago I bought 4 Interstate "Extreme" 6V batteries. What were delivered to the authorized dealer were 4 Interstate "Heavy Duty" 6V batteries.

No big deal. A week later they call for me to pick up the correct batteries; so I do, and take them home.

While installing them I noticed that the new "Extreme" batteries had the same scuff marks (the sort that happen during shipping) as the "Heavy Duty" ones that were returned.

I called the main Interstate office, and they did a bit of cross referencing of the manufacturing number etched onto the battery cases, and found that someone, instead of delivering the correct batteries, simply swapped the labels, thinking that I'd never notice.

The correct batteries are now being delivered, and I can keep the mislabeled ones. There's nothing wrong with the "Heavy Duty" batteries; just wasn't what I paid for.

So to my question.

I now have 4 "Heavy Duty" and 4 "Extreme" batteries. Can I use all 8 to expand my current 4-battery battery bank setup, bearing in mind the half the batteries are slightly different from the other half?

Or, considering that my current 4-battery setup works just fine, the batteries will eventually die, and new batteries are beyond our means (I had to borrow money for these), is there a way to store 4 of them for back-up (for several years)? How long could the back up batteries be expected to last (near new condition, and separately, usable condition) on a shelf, with periodic maintenance?

I hope that Interstate pulls the dealers agreement. What a scum.

 

[Gary RV_Wizard]

Off grid. All we use is for LED camper lights, a Surflo water pump, an inverter for a phone and router, and the spark to start our propane fridge and water heater. No TV, no foot massagers, no disco balls

Just to make sure I got this right, our current setup has four 6V batteries, wired in series and parallel, giving us a 12V system with 210 Ah x 2 = 420 Ah. (?) So adding the other four batteries should be doubling that (420 Ah x 2 = 840 Ah)? Meaning drastically reducing the gas I have to use for the genny on cloudy days?

Basically yes, but didn't you say you had installed the Extremes with 225 AH each rather than 210 for the Heavy Duty? So you have 450 AH now and are contemplating adding 420 AH more for 870 total?

 

[JBK]

Basically yes, but didn't you say you had installed the Extremes with 225 AH each rather than 210 for the Heavy Duty?

Yep, I got it backward in my head.

When adding batteries of dissimilar Ah, do all batteries keep their initial Ah, or do they all revert to the lowest of the batch?

Also, while I'm not sure if linking to another site's forum is allowed (and if not, I'll remove this), I posted basically the same question on a homesteading site, where a few different thoughts were brought up.

Namely that I should not mix batteries, that I should expand my solar, and having more than the four could complicate "balancing".

 

[Gary RV_Wizard]

When adding batteries of dissimilar Ah, do all batteries keep their initial Ah, or do they all revert to the lowest of the batch?

Each contributes its rated capacity.

Namely that I should not mix batteries, that I should expand my solar, and having more than the four could complicate "balancing".

As I stated earlier, mixing batteries isn't ideal, but a small capacity (AH) difference is trivial. And "balancing" is for battery purists, worrying about battery cable lengths and what order the connections are made. If this was a submarine battery bank I'd tell you not to do it, but I think you will survive it ok in your RV. You already own the batteries, so why not get some value from them?

 

[Mark_K5LXP]

If you want to do a deep dive, the disparity you're contending with different batteries having unequal capacity is internal impedance, then secondarily electrolyte diffusion rate. The lighter the load vs capacity, the less these effects will present. Conversely the heavier the load the more pronounced the effect. Then you'd apply your expectation of cycle and calendar life to judge whether those factors matter enough to attempt to mitigate or not. Generally it's not the discharge that's the big problem (I routinely use wildly differing battery sizes in parallel to run things), it's the charge cycle that can impact the longevity of mismatched batteries. People tend to think in terms of the voltages during a charge cycle but currents matter too. Generally with any battery bank the wiring is done to best cancel cable and terminal resistance which almost guarantees that batteries of different capacities will not see an ideal charge profile from a single charge source. Per above, the lighter the current (charge and discharge) relative to the battery capacity the less the effects of the mismatch will be. With a large bank, limited current from the likes of a solar system and tepid loads, keeping a disparate bank "balanced" will be relatively easy. Having that large a bank would offer long run times if needed, but it would otherwise be underutilized and charge efficiencies low. Installation cost would normally be balanced against power delivered but in this case ~50% of it is free, so the tangible benefit is a bit artificially subsidized. Will suggest again the strategy of bank switching which even in a lightly used system can offer improved service life of like or dissimilar bank sizes.

Mark B.
Albuquerque, NM

 

[John From Detroit]

When adding batteries of dissimilar Ah, do all batteries keep their initial Ah, or do they all revert to the lowest of the batch?

In a TRUE socialist economy "Each according to his Ability, Each according to his need" Now when it comes to human economies it's been proven over and a over again.. Don't work (This is not a political post so I won't tell you what does)

But when it comes to batteries in parallel That is PRECISELY how they work
If you put two batteries in parallel and for this I will round shamlesely Say a 100 Amp Hour Group 27 or 28 and a 4D (200 amp hours) well assuming they are fully charged (or same state in any case) The larger battery will provide 2/3 of the amps and the smaller 1/3

And when you re-charge the larger will suck 2/3 and the smaller 1/3

After the first charge/discharge cycle their states of charge will be in perfect lock step.

Why is this? let's switch to water systems


Imagine two wells with pumps one pump is set to 50 PSI and one to 55.
How much water is the first well going to pump? (none for the pressure is too low the higher pressure pump will always KICK in and prevent the lower pressure from working less you are fighting fires and need more GPM)

WSorks the same. Since voltage is determined by State of charge (And a few other things that are same for both batteries if they are side by side) the one with the higher state of charge and thus higher voltage provides ALL the current til lit's SOC matches the other. and on charging the one with the LOWEST SOC sucks all the amps till they match.. And from then on they always match unless one shorts out.

 

[Mark_K5LXP]

And when you re-charge the larger will suck 2/3 and the smaller 1/3

Maybe with perfect/ideal batteries but it doesn't work that way in the real world. It's hard enough to keep a parallel bank of same Ah batteries in balance, mix different capacities and the effects are amplified. Some end up overcharged and some undercharged. A little bit at first, then more as the effects of this cycling cause an ultimate reduction in capacity. For light cycling/low currents the effect may not be significant but then you have a large bank doing very little work. Bank switching obviates this, and PSOC issues as well.

Mark B.
Albuquerque, NM

What happens when connecting two batteries of different amp hour rating in parallel?​

Parallel connecting two batteries of varying amp-hour rating can lead to an uneven distribution of current and voltage between the batteries, because they share different levels of internal resistance. As a result, the larger battery discharges more slowly while a lower capacity discharges faster. In this case, a variety of problem such as a decrease in capacity, a shorter battery life, and potential dangers to safety can happen.

Batteries in series vs parallel: what are the differences?

 

[JBK]

I'm sure given enough time I'd be able to find and learn how to wire a dual bank, but since I've got some expert's ears now, would someone have the time to draw me a wiring diagram?

Would both banks charge at the same time when I have the generator going, and at the same time have one bank powering, for example, the DC lights and water pump?

Is there a way the banks could switch automatically if one gets to, say, 50%?

I can do electric, but my true skill is mashing metal rods into wood.

 

[John From Detroit]

Maybe with perfect/ideal batteries but it doesn't work that way in the real world. It's hard enough to keep a parallel bank of same Ah batteries in balance, mix different capacities and the effects are amplified. Some end up overcharged and some undercharged. A little bit at first, then more as the effects of this cycling cause an ultimate reduction in capacity. For light cycling/low currents the effect may not be significant but then you have a large bank doing very little work. Bank switching obviates this, and PSOC issues as well.

Mark B.
Albuquerque, NM

What happens when connecting two batteries of different amp hour rating in parallel?​

Parallel connecting two batteries of varying amp-hour rating can lead to an uneven distribution of current and voltage between the batteries, because they share different levels of internal resistance. As a result, the larger battery discharges more slowly while a lower capacity discharges faster. In this case, a variety of problem such as a decrease in capacity, a shorter battery life, and potential dangers to safety can happen.

Batteries in series vs parallel: what are the differences?

The battery with the higher state of charge will have a higher voltage and this will overcome the difference in internal resistance. They will thus remain in lock step or so close to it you can not measure the difference.

Now for batteries in SERIES.. Well those need to be "Twins" (As identical as possible) I mean would you replace just one D-Cell in your flashlight?