Capacity testing two used batteries

[Sutty]

I have two retired 5 year old sealed lead acid batteries, 12V and 110Ah each, and I want to check the remaining capacity. One battery wouldn't initially take a charge, but I forced it with a little higher bulk, and a little higher float, overnight, before setting float back down to normal, and leaving it on float for a few days. First time off though, I used a normal car battery charger, and it didn't take a proper charge overnight, with the voltage plummeting as soon as I disconnected the charger. Now though, after a prolonged recovery charge, as described above, using my solar charge controller, it's been holding at near 13V for a few days, just very slowly going down, just as the other one did from the get go. Maybe it was soft sulphated, and it's now been 'fixed'?

Anyway, I now have them both sitting here at about 13V, and I'm wondering if they have anything like the capacity they did when new, but I'm not sure of exactly how to go about checking it.

I have one set up now, ready to go, with a car headlamp connected to the load of my solar charge controller, which will be well within spec for the load. I have the app available to measure the current, but I'm going to use my multi-meter to measure the voltage directly at the battery terminals, rather than trusting the SCC, and the app, because on trial runs, with this reasonable load, being delivered from the solar charge controller, there's quite a lot of volt drop causing the SCC to report low values. I also have a camera, looking at my volt meter, so that when taking a reading for current in the app, I can also keep an eye on the voltage at the same time, which I'll also make a note of.

Tests show the lamp will draw around 4.3 amps, and I can repeatedly take the actual value, whilst writing the time down, so I know how many Ah I've used, and can keep going for the whole day, say for 12 hours, or more if need be, by which time I should have used near half of the listed capacity. Or, terminate early, if I get too low a voltage. I'll take a reading every 5 minutes, for the first few, because I expect the current to fall off quickly, at the beginning, due to initial voltage sag, and then try to take a reading every 15 minutes, but may spread that out, if the current starts holding well, after the start. I'll then just multiply the current, by the fraction of the hour that has elapsed since the last reading, and keep a running tally, which I think should give me the Ah used.

My questions are this:
Is this plan a reasonable approach?
Is aiming for 50%, adequate for a test, or should I go deeper?
How do I know what 50% is, when it's under load, if I terminate early based on voltage? Early practice runs show a significant rebound, or recovery of the voltage, after a 24 hour rest.
Should I just set a target, underload voltage, of say 11.5V, and keep going until then, or is that too high to get the true capacity?
If the trick is to keep going until it's actually dead, voltage drops off a cliff, won't that harm the battery, or is it the only way to know the capacity for sure, and for just one full cycle would be worth it to find out?

I'm thinking I might have to do that, as remaining capacity by voltage seems to be all over the place on the internet, as far as I can see, with most saying to be sure you need the specifics for the battery from the manufacturer, but these are just some generic leisure batteries, so I'm not expecting to find that.

I'd be thankful to hear any thoughts you guys may have.

 

[sunshine_eggo]

I have two retired 5 year old sealed lead acid batteries, 12V and 110Ah each, and I want to check the remaining capacity. One battery wouldn't initially take a charge,

Good luck. Extended sitting a lower state of charge will pretty much destroy a battery's usable capacity even if it will recover voltage.

AGM, GEL or FLA?

but I forced it with a little higher bulk, and a little higher float, overnight, before setting float back down to normal, and leaving it on float for a few days. First time off though, I used a normal car battery charger, and it didn't take a proper charge overnight, with the voltage plummeting as soon as I disconnected the charger. Now though, after a prolonged recovery charge, as described above, using my solar charge controller, it's been holding at near 13V for a few days, just very slowly going down, just as the other one did from the get go. Maybe it was soft sulphated, and it's now been 'fixed'?

Have you floated them @ ~13.8V for a week?

My questions are this:
Is this plan a reasonable approach?

pretty much.

Is aiming for 50%, adequate for a test, or should I go deeper?

No. go to 10.5V and measure true capacity. If that kills them, they're going to die anyway.

How do I know what 50% is, when it's under load,

You don't and you can't.

if I terminate early based on voltage? Early practice runs show a significant rebound, or recovery of the voltage, after a 24 hour rest.

Yep.

Should I just set a target, underload voltage, of say 11.5V, and keep going until then, or is that too high to get the true capacity?

10.5V

If the trick is to keep going until it's actually dead, voltage drops off a cliff,

No.

won't that harm the battery, or is it the only way to know the capacity for sure, and for just one full cycle would be worth it to find out?

This.

I'm thinking I might have to do that, as remaining capacity by voltage seems to be all over the place on the internet, as far as I can see, with most saying to be sure you need the specifics for the battery from the manufacturer, but these are just some generic leisure batteries, so I'm not expecting to find that.

I'd be thankful to hear any thoughts you guys may have.

Does the battery have a RC or reserve capacity rating? If so, can you pull 25A?

 

[Sutty]

Thanks for answering so quickly, I really appreciate it. They didn't sit at a low voltage for 5 years, but were in service for 5 years, and would nearly always have been fully charged, but recently I had to replace them with new, even though they might have been rescuable, which is why I said 'retired'. The reason they had to be replaced is that I screwed up, creating an imbalanced load, which dragged one battery down, and then I had many low sun days, which never gave it that chance to come back up, before I could get back up there to remove the imbalance and rescue it, so it basically got worse and worse. When I got there, one was happily buzzing along at 14V, on a nice day, yet the other was under 12V. Schoolboy error, smh.

It was like this for only a week, at most, but I assumed I'd killed it, or at least severely injured it, with it already being old, so I decided to replace it. Replacing one required that I replace both, so they are equal and matched. I couldn't leave the site without batteries, whilst I tried what I'm trying now, at home, to rescue it, so I had to replace them immediately.

I read in here about extended float periods, and reversing soft sulphation, and thought that might be a possibility, so I've done that, with the early results being promising. The indicator showed black on the bad battery, and green on the good one. After the extended float, the bad one shows fully green again, and as I mentioned, it's now holding at 13V, or thereabouts. This is in stark contrast to the first overnight charge with the car battery charger, where it was down to less than 12.5V before I could even get my volt meter connected, lol. As I mentioned above, I only floated it for few days, three I believe, but I can do it for longer if that will be beneficial.

With regard to the battery type, they are flooded, I can hear liquid electrolyte slosh about if I move them, but I can't top them up, or measure the SG, because they are sealed.

I realised, from my reading here, that holding a voltage, even a good one, isn't the whole truth, which is why I want to do this further test. Having now read you comments, I'll use 10.5V, under my approximate 4A load, and see what happens.

If I may, I'll come back and report the values, because I can't quite grasp how, if we can't know what any given state of charge is, whilst under load, for a given voltage, how do we know that 10.5V is adequately drained, for a full capacity measurement? Wouldn't a higher load have created a further voltage drop, and got me to 10.5V much sooner, simply as a result of the load itself? Like when I put 0.5A on it, fully charged, I instantly lose 0.3V, whereas when I apply 5A, I instantly lose 0.5V.

I didn't know what RC was until just now, and I see that I'd need to pull a constant 25A, until 10.5V, but I have no way of creating a load of that size . Even if I could, I have no way to adjust it, as the voltage drops, to keep it at 25A, so I think I'll have to go with the plan above.

Thanks again. I'll report back with my values in a couple of days.

Cheers

Sutty

 

[Sutty]

Can I stop the discharge, and then resume it tomorrow, if I don't make it by tonight? My 4.3A load isn't going to get there in a day, having started the run at 10:30AM. I'm normally up late, so can likely monitor it until 2AM, but still, I don't think it will get there? Let's see, if capacity is well down, it will, but if it's still half reasonable, then I'm going to have to stop it. I know there will be some voltage recovery, but I'm guessing that will be relatively insignificant in terms of meaningful capacity, with everything soon dropping back down to the levels it was at when I stopped?

 

[sunshine_eggo]

Okay, they're SLA. The fact that you can hear electrolyte sloshing is a good sign.

Given your description, I would be more concerned about the 14V battery than the 12V battery. It's been held at elevated voltage for much longer than is desired. Do you hear sloshing in that one to the same degree? Less chance of sulfation, but a greater chance of electrloyte loss.

Yes, you can stop the discharge.

Concerning RC, it's pretty easy to get an average of around 25A. Start a little high, and you'll end a little low. I have some cheap MSW inverters that I used to power incandescent light bulbs in parallel where I can get pretty close to 25A.

Since your batteries are C20 110, you need to be testing at 110/20 = 5.5A, so you're going

If lead acid batteries are a part of your life (starter batteries, etc.), a digital tester that can measure internal resistance (IR) is an indispensable tool:

Budget version:
https://www.amazon.com/gp/product/B07YD2ZN15 - I have one of these in every car. Great for approximation and comparison between batteries or on the same battery at different times.

Diagnostic version:
https://www.amazon.com/ANCEL-Battery-100-1100-Automotive-Analyzer/dp/B07Q6NBXQG - this one correlates to calibrated lab equipment I use. I regard it as more accurate.

Fully charging both batteries, floating overnight, and then using this tester on them would give you a good comparison between the two. If you have to pick one, IR is the single most important value in determining lead-acid battery health.

 

[Sutty]

Thanks for the extra information. Good to know that I can stop and then restart the test. I'd thought as much, but great to have confirmation.

I do have a couple of spare small inverters, of which I could deploy either, with various loads, to get a much higher current, but then I don't have a clamp meter, and would have to go through my multi-meter, which is 20A max, at which point, I think the leads would be getting pretty warm, and would have a fair old volt drop, with them being fairly long. Load output on the SCC is only 10A, so couldn't use that.

Since your batteries are C20 110, you need to be testing at 110/20 = 5.5A, so you're going

Not sure what you mean above, or if you forgot to carry on?

Given your description, I would be more concerned about the 14V battery than the 12V battery. It's been held at elevated voltage for much longer than is desired. Do you hear sloshing in that one to the same degree? Less chance of sulfation, but a greater chance of electrloyte loss.

It wasn't for very long, that I made the screw up, a few days only, and, perhaps better, based on what you just said, for almost all of the time that the error was in place, there was practically no sun, with it raining every day. It was only up at 14V on the day I got there, because the sun had finally come out, and I was measuring it whilst it was being charged. They slosh the same, and I believe I'm seeing the electrolyte at the bottom of the viewing port where it shows green, but not sure how those indicators work, so I'm not certain.

Diagnostic version:
https://www.amazon.com/ANCEL-Battery-100-1100-Automotive-Analyzer/dp/B07Q6NBXQG

I saw that this had been mentioned and recommended in here before, but I didn't know if I'd have enough need, but I think you're right. I have a couple of garden tractors, three cars, and two batteries at my off grid fishing cabin, and now these two retired ones, which I'm sure I can make use of if they test out okay, so for £45, which is what it is over here in the UK, I'll stump up the cash and get one. I also had concerns that they seemed like a gimmick, and couldn't work as well as they claimed, being so cheap, relatively speaking, but your description that they tally well with your calibrated lab equipment is sufficient reassurance for me. I shall get one.

Thank you again.

 

[sunshine_eggo]

Thanks for the extra information. Good to know that I can stop and then restart the test. I'd thought as much, but great to have confirmation.

I do have a couple of spare small inverters, of which I could deploy either, with various loads, to get a much higher current, but then I don't have a clamp meter, and would have to go through my multi-meter, which is 20A max, at which point, I think the leads would be getting pretty warm, and would have a fair old volt drop, with them being fairly long. Load output on the SCC is only 10A, so couldn't use that.

You could get close enough with a known wattage, i.e., 12V * 25A = 300W.

Not sure what you mean above, or if you forgot to carry on?

Heh. I did trail off. When you see an Ah capacity rating, it is a 20 hour rate (C20), i.e., at constant amperage, it will deliver 110Ah over 20h, so:

110Ah/20h = 5.5A

You are testing to a lower current meaning you should see MORE than 110Ah if the battery meets its rating. You're willing to accept a (5.5-4.6)/5.5 = 16% deviation in your test current to confirm a C20 rate. No reason not to accept an approximation of 25A to confirm an RC rating.

It wasn't for very long, that I made the screw up, a few days only, and, perhaps better, based on what you just said, for almost all of the time that the error was in place, there was practically no sun, with it raining every day. It was only up at 14V on the day I got there, because the sun had finally come out, and I was measuring it whilst it was being charged. They slosh the same, and I believe I'm seeing the electrolyte at the bottom of the viewing port where it shows green, but not sure how those indicators work, so I'm not certain.

If they are both green, that's a good sign. Less time at bad voltage(s) is better.

I saw that this had been mentioned and recommended in here before, but I didn't know if I'd have enough need, but I think you're right. I have a couple of garden tractors, three cars, and two batteries at my off grid fishing cabin, and now these two retired ones, which I'm sure I can make use of if they test out okay, so for £45, which is what it is over here in the UK, I'll stump up the cash and get one. I also had concerns that they seemed like a gimmick, and couldn't work as well as they claimed, being so cheap, relatively speaking, but your description that they tally well with your calibrated lab equipment is sufficient reassurance for me. I shall get one.

Even if those testers aren't absolutely accurate, they are GREAT for comparison. When you buy a new battery, fully charge it and then run the tester on it. That will give you "new" test results. You can then compare future results to the "new" results. I use the red one commercially, and it has been extremely reliable and diagnostically predictive.

 

[Sutty]

Well that answers that one. The voltage just collapsed. I was trying to get my camera to be able to read my meter in the dark, or with only the light from the bulb, and it went off. I thought, that's odd, I set the LVC in the SCC really low. I looked at the meter, to see the voltage climbing rapidly, and then connected to the SCC, to lower the LVC even more and turn the load back on, so I could carry on to 10.5V. Within 2 minutes, the voltage was back down to my last measurement, just before I started messing with lighting for the meter, and then, as I watched, it started to tumble ludicrously quickly, and breezed past my new ultra low LVC at 9V. Almost literally 12 hours after I set off, it was completely depleted. Even rough maths, to check all was well with the calculations, says, 4 x 12 = 48Ah, and the odd little bits gives us the 50.27Ah my spreadsheet says.

Charging now, using my SCC, with my 'panels' being represented by a power supply, which I've restricted to 3.5A and 16V. When it gets back to float, presumably sometime tomorrow afternoon, the current will be well down on that, and I shall leave it like that for a week, as you suggested earlier, to see if it can be improved. I may interrupt it, when it's been on float for a relatively short while, to use my new test meter, which will be here tomorrow, so that I can compare it to one week later. It should be rather interesting I think.

Oh well, this one only has somewhat less than 50% capacity.

I'll address your reply above in another post, because I only just saw it.

Time	Elapsed % of an hr	Current	Voltage	Ah used
10:28​	0.00​	4.43​	12.68​	0.00​
10:29​	1.67​	4.40​	12.60​	0.07​
10:30​	1.67​	4.36​	12.55​	0.15​
10:31​	1.67​	4.34​	12.48​	0.22​
10:32​	1.67​	4.33​	12.46​	0.29​
10:33​	1.67​	4.33​	12.44​	0.36​
10:38​	8.33​	4.32​	12.42​	0.72​
10:44​	10.00​	4.32​	12.40​	1.16​
10:49​	8.33​	4.31​	12.38​	1.52​
10:58​	15.00​	4.31​	12.37​	2.16​
11:10​	20.00​	4.31​	12.36​	3.02​
11:33​	38.33​	4.30​	12.33​	4.67​
12:03​	50.00​	4.29​	12.26​	6.82​
12:33​	50.00​	4.23​	12.19​	8.95​
12:55​	36.67​	4.23​	12.09​	10.50​
13:10​	25.00​	4.22​	12.07​	11.56​
13:50​	66.67​	4.22​	12.04​	14.37​
14:50​	100.00​	4.20​	12.00​	18.58​
15:47​	95.00​	4.18​	11.95​	22.56​
16:51​	106.67​	4.17​	11.89​	27.02​
17:53​	103.33​	4.15​	11.82​	31.31​
19:42​	181.67​	4.13​	11.66​	38.84​
20:44​	103.33​	4.10​	11.55​	43.09​
21:53​	115.00​	4.06​	11.36​	47.78​
22:30​	61.67​	4.00​	11.08​	50.27​

Cheers

Sutty

 

[Sutty]

You could get close enough with a known wattage, i.e., 12V * 25A = 300W.

Yes, thank you.

You are testing to a lower current meaning you should see MORE than 110Ah if the battery meets its rating. You're willing to accept a (5.5-4.6)/5.5 = 16% deviation in your test current to confirm a C20 rate. No reason not to accept an approximation of 25A to confirm an RC rating.

Got you. I didn't even know standard ratings were based on this C20 approach, so I didn't know I was willing to be 16% out, lol. I hadn't been aiming to match that, I just thought a car headlamp was a nice moderate load I could deal with, but thank you for explaining.

If they are both green, that's a good sign. Less time at bad voltage(s) is better.

I thought so, and yet we've just seen the results, or is that rather typical for a 5 year old battery, in constant use?

Even if those testers aren't absolutely accurate, they are GREAT for comparison. When you buy a new battery, fully charge it and then run the tester on it. That will give you "new" test results. You can then compare future results to the "new" results. I use the red one commercially, and it has been extremely reliable and diagnostically predictive.

Excellent. That's the one that has already been despatched. Good idea to use it on a new battery, for comparative purposes.

 

[sunshine_eggo]

SLA and AGM tend to have about 1/2 the cycle life of quality, well maintained flooded cells. To see a 5 year old battery delivering ~50% of rated power after 5 years is no surprise.

Do your batteries specify an equalization voltage? SOME SLA/AGM do, but most don't. You might recover additional capacity.

After fully charging, I'd put it at 13.8V for a week and re-test.

Curious about the second battery. If it's comparable, then I'd attribute it to normal wear and tear. if it's significantly better or worse, I would lean towards imbalance.

 

[Sutty]

SLA and AGM tend to have about 1/2 the cycle life of quality, well maintained flooded cells. To see a 5 year old battery delivering ~50% of rated power after 5 years is no surprise.

Fair enough.

Do your batteries specify an equalization voltage? SOME SLA/AGM do, but most don't. You might recover additional capacity.

I can't find anything specified about these batteries, but I'll write to the supplier, and see what they say. Might just try it anyway, if they don't get back to me. There is a default equalization period in the SCC for sealed, and it's set at 14.6V to run for two hours, on the 28th of each month. Default bulk is 14.4V for two hours anyway, and is invoked every time it's powered on, so I could change that to 14.6V, even though fully charged, and thus run the equivalent of equalisation, but on demand. I'm happy to experiment, and listen for bubbling, outgassing, etc, whilst remembering not to smoke. I can only make them worse, and I'd retired them anyway, but let's see how it goes after a week at float.

After fully charging, I'd put it at 13.8V for a week and re-test.

I already checked the default float setting in the SCC, for sealed, and it is 13.8V, so yes, that's the plan to leave it at that for a week.

Curious about the second battery. If it's comparable, then I'd attribute it to normal wear and tear. if it's significantly better or worse, I would lean towards imbalance.

Me too, and despite having the new tester available, from tomorrow, I will be running the exact same test on that one too, given time. If I can free up my SCC, I can repeat it exactly, but I have a question about that.

Seeing as I have a power supply, where you can set a current limit, or a set voltage, or both, can there be anything wrong with just setting the voltage at exactly 13.8V, measured at the battery, with my meter, and connecting that directly to the battery, once it's already been charged?

If so, I would have my SCC back, to do the test on the second battery, to see how they compare.

Thanks again for all the help.

Cheers

Sutty

 

[Sabre36]

This article is about programming a battery monitor but it has instructions for how to do a 20h capacity test,

Making Your Battery Monitor More Accurate



.

 

[sunshine_eggo]

If you are talking something like a lab benchtop power supply - the typical 30V/10A unit, yes, absolutely, just connect directly to battery.

 

[Sutty]

This article is about programming a battery monitor but it has instructions for how to do a 20h capacity test,

Thank you, I'll have a good read later, At a glance that could be handy for my cabin.

 

[Sutty]

If you are talking something like a lab benchtop power supply - the typical 30V/10A unit, yes, absolutely, just connect directly to battery.

Yes, it is almost exactly that, but sadly only 5A and 20V, but it has been doing a fine job, so far, of simulating my panels, albeit at a low output current. As of about 5 minutes ago, I just happened to be watching, and the SCC switched to float, the current dropped to about 1A, and my meter changed to 13.8V, at the battery. I imagine the current will tail off too, in this phase, given time, because the other day it dropped back to about 0.25A. Thanks for the confirmation.

 

[Sutty]

Spotted something with my power supply that I hadn't noticed before, which I believe to be good. I set it to 13.8V, with a low current limit, and when I connected it, I noticed that CC, had lit up at the left, and the voltage was a little depressed. As I wound up the current, so it was allowed more than it needed, it flicked over to CV mode, at the right, automatically, and the voltage went back up to 13.8V. When I checked at the battery, despite there being 1.4A flowing, it read 13.8V too. I was a little surprised, as my available wire gauge was not that great, so I expected a little drop, but there was none apparent. I put another meter across the wire lengths, to measure the potential difference, end to end, and got only 20mV, and 18mV respectively, so no surprise then that there was no appreciable difference, between the supply reading and the meter on the battery. Length is pretty short, to be fair.

Still quite surprised that my repurposed speaker wire shows so little drop off at what was, by then, 1.1A, though I'm sure I could look it up on a table, if only I knew the actual gauge, lol.

Anyway, here is a little picture of CV mode in operation, which I'm assuming is the correct mode to maintain float for the week?



Cheers

Sutty

 

[Sutty]

Test two complete, on the other battery, and the results are astonishingly similar. The test was slightly different, in that I saw 10.5V fly by, this time, because I was ready for it and watching, but as with the first battery the plummet happened from just about 11V. The other difference was that I slept whilst much of it ran, so there is a big gap between 2AM and 9:35AM, but in both cases, my Ah field was using the average current, from the last two readings, rather than just the last one, and together with the time difference that was used to calculate the cumulative Ah used, so I think it's still going to be close. Indeed, as an experiment, I just checked how the calculation would come out with only about 5 data points. Two at the beginning to get the spreadsheet going, one after half an hour, and two right from the end, to finish off the spreadsheet. The calculation only changes by roughly 0.5Ah. On this basis, I think a few values, as long as you can be ready for when it ends, will do. Beginning, somewhere in the middle and the end, will give you a value near enough the mark.

Results below. It would seem the batteries are rather equally rubbish now. I guess 5 years of none stop daily use is about all you can expect from a bog standard, relatively cheap, sealed, flooded, lead acid battery.

Time	Elapsed % of an hr	Current	Voltage	Ah used
00:01​	0.00​	4.48​	12.83​	0.00​
00:02​	1.67​	4.39​	12.66​	0.07​
00:03​	1.67​	4.36​	12.62​	0.15​
00:04​	1.67​	4.35​	12.61​	0.22​
00:11​	11.67​	4.33​	12.55​	0.73​
00:30​	31.67​	4.31​	12.45​	2.09​
01:00​	50.00​	4.30​	12.36​	4.25​
01:30​	50.00​	4.28​	12.28​	6.39​
02:00​	50.00​	4.27​	12.20​	8.53​
09:35​	758.33​	4.14​	11.63​	40.42​
10:08​	55.00​	4.12​	11.55​	42.69​
10:35​	45.00​	4.12​	11.47​	44.54​
11:16​	68.33​	4.07​	11.32​	47.34​
11:30​	23.33​	4.00​	11.25​	48.28​
11:36​	10.00​	4.00​	11.20​	48.68​
11:46​	16.67​	3.98​	11.10​	49.35​
11:51​	8.33​	3.83​	10.50​	49.67​

I'll come back to the Ancel tester, after more practice, and after the batteries have both floated for a week or so, and then rested for a couple of days. I'm going to bring this last one back up now to a full charge, then parallel it to the the other one, currently on float, with high quality leads, 35 sq mm, and float them both together for the week, seeing as they are all but identical.

Cheers

Sutty

 

[Sutty]

My Ancel tester is clearly faulty, and I have written to them, describing the symptoms. The same test, twice in a row, on the same battery, would report wildly different values for SOH, ranging from good, 100%, to 7%, replace. The IR, on which I suppose must of it is based, would also be all over the place, until today. Today, trying more tests, on any battery, always reports exactly 100.00 mOhms, which clearly cannot be true. It's probably the limit of that field, for what is effectively open circuit for that test. I strongly suspect what was a loose connection, somewhere, which has now come away completely. I also suspect I could repair it, if I hadn't put it in the hands of the supplier, and the manufacturer, to confirm my suspicions. Don't want to take it apart to examine the lead connections, or even disassemble the crocodile clips, because that would obviously invalidate the warranty. Doubt it can be at the clip end anyway, as you'll see below.

I was hoping my batteries would report around 50% SOH, thus confirming my own observations, but anything from 30% to 70% would have been believable, if it were reasonably consistent. Mine said, CCA 800, tested CCA 14. I then tested again, and got, CCA 800, tested CCA, 1440, lol. I think at that point the loose wire must have been shorting across inside of the unit, giving an incredibly low IR, and a very good battery result, which also had a SOH of 100%.

Who knows, but it's definitely faulty, and it's annoying that I can't look at it myself, but I don't want to waste £45.

 

[Sutty]

Couldn't resist. Just two screws, and I thought, if I remove them, and it doesn't easily come apart, then I won't look and I'll return the screws, but if that's all that keeps the case closed, I'll open it and take a peek. Opposite end to the two screws were just two clips, so it was simplicity itself to tease it apart, with zero marks, or any damage to the case whatsoever. I didn't even have to put my finger nails between the case halves, I could just open it from the screw end. I've now put it back together, perfectly, awaiting their response, but I don't know whether to report what I found or not.

Inside, a rather large, 5W, 10 Ohm resistor, floating free at one end. Clearly it was partially attached when I received it, hence the odd or very odd, variable readings, but it's now completely free at one end, hence my readings of 100.00 mOhms, every time. I'm pretty sure I could re-solder it, should they refuse my claim, even though there is little of the leg poking out of the ceramic, or whatever the material. It's a fairly heavy component, and fits, floating in a rectangular hole, in the board, held there only by its legs. A lot of strain for those very small leads, so I'm not surprised it could happen, especially if it had been flung around by Amazon as they delivered it.

 

[sunshine_eggo]

Yikes, sorry to hear that! I suspect it is a factory defect. I have dropped mine on concrete and banged it around quite a bit. It is WELL used, and it's quite consistent.

Whelp... 50Ah is 50Ah, and they're well matched on capacity, and their voltages look pretty darn close at a given discharge point. If the IR tester comes back comparable, I'd say it's worth using them for something UNLESS they have more value as returned cores for purchasing new batteries.