Solar Inverter Low-Voltage Warning/Shutdown

[Josh M.]

I have an Eco-Worthy 1500W Off Grid Pure Sine Wave Inverter and have a question concerning low-voltage shutdown.

I am going to be out of town for most of the day and won't be back until after dark. My solar will run all day and power my house but will not last through the evening (after sundown) and into the night. Once the voltage drops low enough, my inverter starts beeping with the low-voltage warning and eventually the power inside shuts off. The low-voltage warning continues until I actually shut off the inverter.

My question is this....

Once the power automatically shuts down in my house and is no longer drawing off of my battery bank, if the inverter's On/Off switch is not physically turned off and the low-voltage warning keeps beeping, will this continue to drain my battery bank until the inverter switch is turned off? I just don't want to damage my battery bank or my inverter by letting the warning signal continue to go off. I am not using LifePO batteries, just sealed lead deep cycle batteries.



Thanks for any help!

 

[MichaelK]

Since your inverter is still displaying a warning message, then you know it's still consuming power, though it's likely to be significantly less then what it's consuming when it's actually inverting. Really, you are going to have to determine this yourself. Using a clamp meter, you can clamp one of the battery cables going to the inverter and measure how many amps are powering the warning lights.

Honestly, if the battery is draining even before you go to bed, it is drasticly too small to power your load. What is the actual load while away from home? Is it running the refrigerator? I'd guestimate you need at least a very minimum of 1.5kWh to run the inverter and just a refrigerator in 24hours, then you need at least (1500W/12V) X 2xcapacity = 250Ah battery. And that's bare, bare minimum.

 

[Josh M.]

If we are not at the homestead, and it's not too warm outside, we only have a fridge being powered, We unplug everything else like fans, satellite internet, computers, etc., to make sure our energy consumption is at a minimum. I assumed the inverter's warning tone and small 3 digit display would be pulling some sort of power, but hoped it would be insignificant enough of a draw that I wouldn't have to worry about my batteries being damaged over the course of the few hours after the system automatically shuts down.

I unfortunately don't have any meters of any sort to measure the amp draw of the warning signal and display.

I'm definitely aware my system is undersized for my needs. Due to some unforeseen financial issues just before we made the move out here to the homestead, we had to severely cut back on a number of areas. Even though we still made the solar a priority, we still ended up with an undersized system. We have 8 100w panels and 2 105Ah sealed lead deep cycle batteries set up for 24v. In a few weeks, I will be able to upgrade that to 4 batteries. And hopefully in the next couple months, up to 6 batteries.

 

[MichaelK]

I'm sorry to hear about your situation.

I could make a couple of suggestions that hopefully could save you a bit of money.

Instead of buying more sealed batteries, I'd suggest waiting till you have the money to upgrade, and then selling what you already have, and buy golf-cart batteries instead. Costco has a 6V 210Ah battery selling now for 99$. So, for somewhat more than adding one additional string at 105Ah, you'd be getting 210Ah. Just get a gallon of distilled water to top off the batteries every couple of months. Perhaps later, you could add a second 210Ah string once finances allow. Don't though mix different Ah sized batteries.

Instead of 100W 12V panels, get grid-tie panels instead. Shop locally on Craigslist and find cash and carry sellers. Expect to get 4W/$ buying panels this way. You don't have to get rid of your 100W panels though. Just wire the parallel strings such that the Vmp of each string is <5% different. More solar will help you get to absolutely full charge each and every day.

Rather than leaving the frig on and shutting everything else off, have you tried shutting off the frig while leaving everything else on? You can fill up the frig and freezer sections with water bottles in the early morning to increase the mass, and then let that extra mass help you get through the night without things thawing. I'd use a bottle size that would be solidly frozen by sunset.

Hope that we'll be able to continue to help you as you progress.

 

[Josh M.]

I really appreciate the info! Very helpful for sure.
I'll have to consider the golf cart batteries (though I don't have a Costco membership), but since I run a 24v system, I'd need 4 of the 6v batteries ($400). Granted, that would give me 840Ah vs. 4 of my current batteries at 420Ah which is way better. But, I already have 3 of my sealed lead batteries though (just can't use the 3rd to make the 24v) so I'm buying one more at the cost of $104 to complete the 4ea. 24v battery bank. Then 2 more in a couple months (another $210). So, I'd have a 24v 6 battery bank at 630Ah. I have a buddy also living off-grid that said his 8 100w panels charged his 6 batteries fairly efficiently. It was when he bumped up to 8 batteries when he had issues with getting a full charge each day.
Also, I was really trying to avoid the unsealed battery maintenance and ventilation issues. My home is a 5th wheel RV right now so I don't have any sort of outside storage area where I could keep that type of battery. But again, 840Ah is very enticing! Will definitely have to think that one through.

I have looked into larger watt used panels but it seems most of what I find has damage or flaws in them that degrade the efficiency, so not really sure what to do there. The only time I have heard the term grid-tie, it has referred to being tied into the grid, which is absolutely not an option for us as there are no available utilities in our area. And even if there was, we moved off-grid to be off-grid and don't want to feed the utility companies any more than we have for all these years.

I could definitely shut the fridge off using your suggestion with the water bottles. I'll give that a try.

 

[Doggydogworld]

I'll have to consider the golf cart batteries (though I don't have a Costco membership), but since I run a 24v system, I'd need 4 of the 6v batteries ($400). Granted, that would give me 840Ah

Four 210Ah 6V batteries in series to make 24V are still 210Ah.

I have looked into larger watt used panels but it seems most of what I find has damage or flaws in them that degrade the efficiency, so not really sure what to do there. The only time I have heard the term grid-tie, it has referred to being tied into the grid, which is absolutely not an option for us as there are no available utilities in our area.

The panels don't have to be grid tied. But larger panels designed for rooftop and such tend to be much cheaper than the 100W panels designed sold for campers and picnicking. The large panels are usually higher voltage, so you generally need a MPPT type controller which offsets some of the savings.

I agree 25 cent/Watt only applies to used panels, so lots of caveat emptor. But you can find ones in good shape. I also see free panels from time to time, mostly in CA. I recently posted about some in Poway (north of San Diego).

I could definitely shut the fridge off using your suggestion with the water bottles. I'll give that a try.

Let us know how this works. Use thermometers. Don't put warm food into it in the evening or first thing in the morning.

I'd freeze water bottles during the day then put them in the refrigerator section at night. I'd try to find something that freezes around 5F to keep on the freezer side. Maybe water bottles with a weak antifreeze mixture? You want to make sure they get completely frozen during the day, then they'll hold the freezer compartment near 5F until fully melted.

 

[Josh M.]

Four 210Ah 6V batteries in series to make 24V are still 210Ah.

I'm still very new to solar so please forgive my ignorance with this. The whole in Series vs. in Parallel still confuses me at times.
So, you're saying that even if I get 4 105Ah batteries hooked up to make a 24v battery bank, I'll still only have 105Ah? If this is the case, what good does it do me to continue to expand the size of my battery bank? If I have 4 or 6 batteries, vs. the two I have hooked up now, if I maintain the 24 v system, do I not gain more battery storage? I assumed more batteries meant more energy storage.

The panels don't have to be grid tied. But larger panels designed for rooftop and such tend to be much cheaper than the 100W panels designed sold for campers and outdoor. The large panels are usually higher voltage, so you generally need a MPPT type controller which offsets some of the savings.

Oh, ok. That makes sense. That'll have to be a future investment then because I currently do not have an MPPT controller.

 

[Doggydogworld]

I assumed more batteries meant more energy storage

It does. But Ah is not energy. Wh is energy. Wh is V * Ah. See below for some numbers.

So, you're saying that even if I get 4 105Ah batteries hooked up to make a 24v battery bank, I'll still only have 105Ah?

Four 12V 105Ah batteries in a 2S2P setup would be 24V 210Ah.

Parallel --> Volts stay the same, add Amps together
Series --> Add Volts together, Amps stay the same
(hours are always the same, unless you're in the waiting room at the doctor's office)

Right now you have two 12V 105Ah batteries hooked in series. So add the Volts. You have 24V and 105Ah.

Four 12V 105Ah batteries in series is 48V 105Ah
Four 12V 105Ah batteries in parallel is 12V 420Ah.
To get 24V from four 12V batteries you connect them in both series and parallel, i.e. 2S2P. This gives you 24V 210Ah.

Energy is V times Ah or just Watt-hours (Wh). Your two-battery setup has 24V * 105Ah = 2520 Wh.
Four 12V 105Ah batteries have 5040 Wh, no matter how you hook them up, because:
48V * 105Ah = 24V * 210Ah = 12V * 420Ah = 5040 Wh

A 6V 210 Ah battery has the same energy capacity as a 12V 105Ah one.
Four 6V 210Ah in series is 24V 210Ah, same as a 2S2P with four of your batteries.

 

[Josh M.]

OK, great! Shockingly, I actually understood that, lol! That's the best explanation I have found online so far, Thanks for that!

So, one more question (for now, lol!)...

Once I get my 4 batteries hooked up in an 2S2P config, will that essentially double the amount of time my battery charge will last? Or is that too simplistic of a view?

 

[MichaelK]

Once I get my 4 batteries hooked up in an 2S2P config, will that essentially double the amount of time my battery charge will last? Or is that too simplistic of a view?

Yes, it's too simplistic. You need to remember that as you raise battery capacity, you need a corresponding increase in solar charging. A good rule of thumb is to divide the Ah by 8 to get the number of amps the battery should be charged at. Chronic undercharging is really the weak link for lead-acid batteries. Under charge them and they will die a premature death. Charge them at max and they will give you many years of faithful service.

DDW is correct that the 4W/$ quote is for used panels, but what I've found with real-world testing is most of the "used" panels I've bought are higher quality and higher output than the "new" panels I paid retail for. I'm never going to pay retail for panels ever again.

As you add more and more parallel strings of batteries, it becomes harder and harder to keep each individual string in balance with each other, so one string will get more charge, and another less. As the number of parallel strings gets larger and larger, the imbalance problem gets larger and larger. This leads to an earlier battery death.

One reason for recommending larger golf-cart batteries is you get the same capacity in one string as you would two, so there can't be any inbalance. Double that and you've have to have four parallel strings of those 12V batteries.

 

[Doggydogworld]

A fully charged 5040 Wh system like the 2S2P example will indeed power a given load twice as long as your existing 2520 Wh battery pack. But "fully charged" is the key phrase. As Michael points out the bigger pack needs twice as much solar power to get to fully charged.

Sizing everything correctly takes work and planning. Add stuff without a good plan and you'll end up with a panel/controller combo that doesn't fully charge your battery, or batteries that can't supply all the current the inverter asks for, or some other problem. And when you add stuff to fix one problem, another will crop up.

First figure out your total consumption (in kWh) per day or week. This varies by season. Also figure out nighttime consumption and peak instantaneous demand (e.g. AC kicks on when microwave and other stuff are running).

Very crudely, total consumption determines panel size, overnight consumption determines battery size and peak demand determines inverter size. But as mentioned above, the components also have to match each other.

The second step is to reduce total consumption, overnight consumption and peak demand. LED lights reduce both total and overnight consumption. The water bottle fridge trick wont reduce total consumption, but can shift that consumption into the daytime hours and save battery cost. Turning the AC off to run the microwave or whatever will reduce demand peaks and save inverter cost. Running the fridge on 12V (if it can) also saves inverter cost.

Reducing and shifting demand is generally much, much cheaper than adding panels, batteries, inverters and such.

The third step is to size the components to handle your total consumption, overnight consumption and peak demand. Make sure all the components match up with each other.

The final step is to have a backup plan for long cloudy stretches, severe cold snaps, etc. A system that works 95% of the time with a cheap generator for unusual days will cost a lot less than a system which supplies all your needs all the time.

The final, final step is to fully sketch out your planned system and submit it here so the real experts can give you suggestions.

 

[Josh M.]

You guys have been a huge help!! I really appreciate it!! I will move on your suggestions the best I can with what I have and what I can afford to pick up.

We do eventually want a system that will supply all of our needs but I know that will come at a cost and will take some time. And we still need to build a house, lol!

As for the fridge, it's a mid-sized residential fridge that does not run on 12v or propane (like a normal RV fridge) so we're kinda stuck there.

Our night time consumption in the RV right now consists of the fridge, a humidifier, on-demand water pump, and our phone chargers. The only other thing we have plugged in at night is our Sleep Number bed, but that only runs for a brief moment while we adjust the air right at bed time. But even with the phone chargers, we could easily shift that to charging them during the late part of the day before the sun goes down so we don't draw power overnight.

My current solar set up, if I did not say it already, consists of 8ea 100W 12v solar panels hooked up in series, a 60a charge controller (not MPPT), a 4-string combiner box, a 3000w peak/1500w continuous inverter , and 2ea 12v 105Ah sealed lead acid deep cycle batteries hooked up for 24v (soon to be 4 batteries). All from Eco-Worthy with the exception of the batteries which I got from O'Reilly.

During the day, we have zero issues with solar power deficiency, even on mostly cloudy days. We have been running a box fan on warmer days, my laptop for work 10 hours a day, my wife's PC for 3-4 hours, the fridge, Starlink Internet, and water pump. The RV is fully outfitted with LED lights throughout.

We have a 5500w generator that we have been using every night because we have needed to run the A/C at night (we've also had to use it during the day at times over this past month due to higher than normal temps). With temps finally dropping, we shouldn't need to run the A/C but we still need it for the fridge, humidifier, and water pump. But we're hoping with the additional batteries, we can run these few things (minus the A/C) overnight on the batteries. The gas cost on the generator is killing us right now to the tune of $360 a month so we really want to limit how much we have to use it.

 

[Doggydogworld]

Can you post brand/model and/or specs for the panels, controller and batteries? Just offhand, eight 100W panels in series sounds like way too much voltage for a PWM controller to handle efficiently. They should probably be set up as 2S4P. That might require some cheap fuses and maybe extra wires.

Phone charging won't move the needle - a phone battery is something like 10 Wh. A residential fridge uses >100x that much in a day.

Humidifier shouldn't use much, the ones I remember just run a small fan over a half-submerged wheel. But see if you can find its consumption anyway.

In theory your system should be able to run your daytime loads and power the fridge all night. I don't know why you get that low voltage warning so soon. Does your Eco-Worthy inverter show battery voltage on an LCD panel? If so, record the voltage at midday, then just again after sunset (without the generator running) then again every half-hour or so until it starts beeping. Maybe we can get an idea what's going on with the batteries despite the lack of meters.

To address your original question, Eco-Worthy claims a mere 12W power consumption for their 1500W inverter. Seems that should drop to near-zero once it shuts down the loads. But even if I'm wrong, your batteries should be able to supply 12W for hours.

That said, you really don't want to drain lead-acid batteries very often. 50% discharge is ideal. I'd want to figure out what's going wrong before I hooked up any more batteries. Especially new ones I'd just paid for.

 

[Josh M.]

Can you post brand/model and/or specs for the panels, controller and batteries? Just offhand, eight 100W panels in series sounds like way too much voltage for a PWM controller to handle efficiently. They should probably be set up as 2S4P. That might require some cheap fuses and maybe extra wires.

Phone charging won't move the needle - a phone battery is something like 10 Wh. A residential fridge uses >100x that much in a day.

Humidifier shouldn't use much, the ones I remember just run a small fan over a half-submerged wheel. But see if you can find its consumption anyway.

In theory your system should be able to run your daytime loads and power the fridge all night. I don't know why you get that low voltage warning so soon. Does your Eco-Worthy inverter show battery voltage on an LCD panel? If so, record the voltage at midday, then just again after sunset (without the generator running) then again every half-hour or so until it starts beeping. Maybe we can get an idea what's going on with the batteries despite the lack of meters.

At this very moment, 3pm, just after the peak sun of the day, full sun no clouds, the charge controller is showing 28.4v coming in from the panels. Inverter displays 28v. I have the fridge, internet, and my 17" laptop drawing power.
By about 4:30pm to 5pm, the inverter typically shows about 25v to 25.4v. once the sun dips deep on the western horizon, it drops to about 23.5v. Once my inverter hits 22v or less, the low-voltage alarm starts. By about 19-ish volts, power automatically shuts off to the RV. If I'm extra cautious with power consumption, after a day with these conditions, after I shut down my work laptop and unplug the satellite internet, and just have the fridge running and the occasional draw from the on-demand water pump, I can maybe get to about 9:30pm to 10pm before I lose solar power.

I have thought since the beginning that my low-voltage alarm comes on too soon at 22v. Considering 50% of my battery bank voltage would be 12v. As far as I know, I do not believe there is any way to adjust when the alarm signals.

To address your original question, Eco-Worthy claims a mere 12W power consumption for their 1500W inverter. Seems that should drop to near-zero once it shuts down the loads. But even if I'm wrong, your batteries should be able to supply 12W for hours.

That said, you really don't want to drain lead-acid batteries very often. 50% discharge is ideal. I'd want to figure out what's going wrong before I hooked up any more batteries. Especially new ones I'd just paid for.

 

[Doggydogworld]

Combiner box probably means your panels are 2S4P, which is what you want. How are your panels mounted -- flat, tilted or moveable?

I assume your charge controller is also from Eco-Worthy? Is there anything connected to the load terminals (the two on the far right) or just the solar and battery terminals? You can cycle through different screens by pressing the left button. The 1st (default) screen shows battery voltage plus a bunch of icons. The 2nd screen is panel voltage and the 3rd is panel current. The 6th screen is Charging Amp-hours, which I think might be total Ah sent to the battery so far that day. Let's see what screens 1, 2, 3 and 6 say at midday and again at 4pm, 5pm and 6pm.

It sounds like your battery is already discharging by 4:00-4:30pm, which is earlier than I'd expect. What time is your sunset these days?

19V is very low for a 24V battery. This good info page has some lead-acid voltage charts (scroll down to the 24V section) plus other info like depth of discharge (DoD) vs. cycle life (scroll down more). Here's the 24V sealed lead acid voltage chart:



This is "resting voltage", you have to disconnect the battery and let it sit a couple hours to measure it. Voltage will be higher when charging and lower when discharging. But it gives a general idea of how 100% full to 0% empty is a pretty narrow voltage range.

I'm really interested in what screens 1, 2, 3 and 6 say at midday and as the sun gets lower.

 

[MichaelK]

OK, something odd is going on here. No way the battery should be dropping down to 23.5V right at sunset. Either the charging parameters are not set correctly, or those batteries are already dying. A good 24V battery should be charging up at up to ~29.4V to 29.6V at full charge charge. Just reaching 28V is suspicious to me. Each panel should be outputting ~17.3Vmp, so two in series would be 34V. So I'd expect when charging, they'd reach 29.4-29.6V?

Part of the problem might be the controller is just PWM. So the full output of the panels never reaches the batteries. What I suspect might be happening at this point is that these batteries are already dying, and can't hold a charge any more. This is the real-world ramification of poor design, and going cheap.

Sadly, I understand that your financial situation does not immediately allow you to make the proper upgrades to make this work as intended. In the short-term, what I could suggest you do is shut off everything, including the inverter, and focus your complete attention on getting the batteries fully charged. They might have already been permanently damaged, but you might get lucky. Test the state of charge at the end of the day with the batteries disconnected and rested for a couple of hours. If those batteries are not at 25.6-25.7V, then assume they are failing.

I'm very sorry, but the reality is that good solar isn't cheap, and cheap solar isn't good. You've had to learn this the hard way.

 

[Josh M.]

Combiner box probably means your panels are 2S4P, which is what you want. How are your panels mounted -- flat, tilted or moveable?

I believe that's correct. Of the 8, each set of 2 are connected together and to one port in the combiner.
Currently they are angled and only semi-moveable. I will be building a rack to mount them all on together in a couple weeks and then I will be able to shift the rack manually to track the sun's path better throughout the day.

I assume your charge controller is also from Eco-Worthy? Is there anything connected to the load terminals (the two on the far right) or just the solar and battery terminals? You can cycle through different screens by pressing the left button. The 1st (default) screen shows battery voltage plus a bunch of icons. The 2nd screen is panel voltage and the 3rd is panel current. The 6th screen is Charging Amp-hours, which I think might be total Ah sent to the battery so far that day. Let's see what screens 1, 2, 3 and 6 say at midday and again at 4pm, 5pm and 6pm.

Yes, everything except the batteries are from Eco-worthy.

So, I didn't get the midday reading since it was already past that time, but here I got 4:30, 5:30, & 6:30 readings.
4:30
Screen 1(S1) - 28.4v
S2 - 28.5v
S3 - 5.52A
S6 - 2.084k Ah

5:30
S1 - 25.6v
S2 - 25.8v
S3 - 2.96A
S6 - 2.087k Ah

6:30
S1 - 24.6v
S2 - 24.7v
S3 - 0.00A
S6 - 2.088k Ah

It sounds like your battery is already discharging by 4:00-4:30pm, which is earlier than I'd expect. What time is your sunset these days?

Sunset is somewhere around 6:15-ish.

19V is very low for a 24V battery. This good info page has some lead-acid voltage charts (scroll down to the 24V section) plus other info like depth of discharge (DoD) vs. cycle life (scroll down more). Here's the 24V sealed lead acid voltage chart:

View attachment 112161

This is "resting voltage", you have to disconnect the battery and let it sit a couple hours to measure it. Voltage will be higher when charging and lower when discharging. But it gives a general idea of how 100% full to 0% empty is a pretty narrow voltage range.

I'm really interested in what screens 1, 2, 3 and 6 say at midday and as the sun gets lower.

 

[Josh M.]

OK, something odd is going on here. No way the battery should be dropping down to 23.5V right at sunset. Either the charging parameters are not set correctly, or those batteries are already dying. A good 24V battery should be charging up at up to ~29.4V to 29.6V at full charge charge. Just reaching 28V is suspicious to me. Each panel should be outputting ~17.3Vmp, so two in series would be 34V. So I'd expect when charging, they'd reach 29.4-29.6V?

Part of the problem might be the controller is just PWM. So the full output of the panels never reaches the batteries. What I suspect might be happening at this point is that these batteries are already dying, and can't hold a charge any more. This is the real-world ramification of poor design, and going cheap.

Sadly, I understand that your financial situation does not immediately allow you to make the proper upgrades to make this work as intended. In the short-term, what I could suggest you do is shut off everything, including the inverter, and focus your complete attention on getting the batteries fully charged. They might have already been permanently damaged, but you might get lucky. Test the state of charge at the end of the day with the batteries disconnected and rested for a couple of hours. If those batteries are not at 25.6-25.7V, then assume they are failing.

I'm very sorry, but the reality is that good solar isn't cheap, and cheap solar isn't good. You've had to learn this the hard way.

I just posted some readings that Doggydog asked for. Those are more accurate than my guessing from memory earlier.

I really hope these batteries aren't dying already! That would be a huge blow to our situation out here!

I'll see if I can arrange to just let my batteries charge for a full day and see what readings I get then.

I know, I didnt want to go cheap but we needed something and there was just no way for us to afford those incredibly expensive batteries that come from the solar companies and I had no idea something like a 6v golf-cart battery would be better than the deep cycle batteries I bought.

 

[Doggydogworld]

~150W coming out of the panels at 4:30pm sounds low to me. Could be a lot of things -- sun/panel angle, shading, the PWM thinking the battery is full. Let's see what a midday reading looks like. You won't get the full 800W with a PWM, but the currents should at least be higher. 2 kWh supplied to the battery also sounds low, but it depends on how much went out through the inverter. Unfortunately you don't have the equipment to measure that.

I agree with @MichaelK that the battery voltages are the bigger issue at this point. I'd avoid hooking any more batteries up until you figure that part out. Since you run on generator in the evening anyway that'd be a good time to disconnect the batteries and let them rest a few hours so you can get an accurate voltage / SOC reading. You'll need a meter. You can buy a simple voltmeter for ~5 bucks, but you really need a clamp meter that also measures AC and DC current. Cheap ones are 20 bucks online. Don't get the $15 Harbor Freight or $20 WalMart meter that only measure AC current.

You might also pick up a Kill A Watt meter. They're good for measuring 120VAC consumption for things that cycle on and off like your fridge, humidifier, water pump, AC and box fan. New ones are $25-30 but you might find a used one cheap on Craigslist or eBay.

You might be able to borrow some of this stuff, too.

 

[MichaelK]

Thank you for the data. It needs a bit more explanation though? What is the difference between screen 1 and screen 2? Where are these voltages being measured? Screen #3 is the amps coming into the battery? Screen #6 though is a bit confusing? Was that supposed to be daily production in kWh? 2088Wh would be ~2.6sunhours out of 800W of panels.

The way I would interpret this is that while the sun is still up the batteries are charging up to ~28.4V, which is standard I believe for gel batteries. What does your battery manufacturer state as the best charging voltage? After sunset though the voltage is rapidly dropping down to only 24.6V?
What kind of load is on the batteries from 5:30pm till 6:30pm? Is the refrigerator running? With four parallel strings of panels, the max theroretical amperage would be 23.12A, but in the real-world, not likely to ever be over 19-20A. Can you remember what the highest amperage was that ever went into the battery?

Really the very best way to determine if your batteries are still OK, is remove all loads, and shut off the inverter, and try to get the battery up to full charge, then disconnect it and check the voltage manually an hour or two after sunset. Do NOT check the voltage while any load at all is on the battery. If at that point you are not seeing 25.6V or so, then assume the batteries are damaged. You can't equilize them, so there is not much else to do expect trade them in.
4:30
Screen 1(S1) - 28.4v
S2 - 28.5v
S3 - 5.52A
S6 - 2.084k Ah
5:30
S1 - 25.6v
S2 - 25.8v
S3 - 2.96A
S6 - 2.087k Ah

6:30
S1 - 24.6v
S2 - 24.7v
S3 - 0.00A
S6 - 2.088k Ah