How To Check A Leisure Battery's True State? (1 Viewer)

[PhilandMena]

You have used 23Ah and your resting voltage after consuming 23Ah is 12.56V. Using the chart below, 12.56V represents a SoC of approximately 70%. Therefore, you have consumed 30% of the battery capacity. Since you have consumed 23Ah and this represents 30% of your capacity, you can now calculate that your true battery capacity is (23/30)*100 = 77Ah.

View attachment 868414

Ian

Your chart is for AGM. The charts I've seen for lead acid wet cell show 100% at 12.7.

 

[PhilandMena]

Without sounding thick, what is the 90 in your equation?

Remaining S.O.C according to charge chart for lead acid wet cell battery. I.e.90%.

 

[bigtwin]

Your chart is for AGM. The charts I've seen for lead acid wet cell show 100% at 12.7.

Most leisure batteries are sealed lead acid.

In any case, I was demonstrating the calculation method.

Ian

 

[PhilandMena]

Most leisure batteries are sealed lead acid.

In any case, I was demonstrating the calculation method.

Ian

I tried that method and it did not make sense. 23/10x100=230. I did raise this in my original thread and never did get an explanation or find out how much capacity I used. Batteries were changed last year and were performing well when replaced.

 

[bigtwin]

I tried that method and it did not make sense. 23/10x100=230. I did raise this in my original thread and never did get an explanation or find out how much capacity I used. Batteries were changed last year and were performing well when replaced.

Why divide by 10? In the belief that 12.56V represents a 10% discharge? Which chart suggests that?

Ian

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[PhilandMena]

Why divide by 10? In the belief that 12.56V represents a 10% discharge? Which chart suggests that?

Ian

There are many charts that show that. Here's one, I'm out celebrating with family at present so will post again tomorrow.

https://cdn.shopify.com/s/files/1/2637/1868/files/image4.png?v=1674584695

 

[bigtwin]

There are many charts that show that. Here's one, I'm out celebrating with family at present so will post again tomorrow.

https://cdn.shopify.com/s/files/1/2637/1868/files/image4.png?v=1674584695

Ahh, yes, the wet lead chart shows 12.56V as only 10% discharged.

The error you made in your calculation below was assuming that your ’remaining’ 77Ah was a given when, in fact, that is the variable that you’re attempting to establish. The known facts are that you took 23Ah out of the battery and that, according to the wet chart represents a discharge of 23Ah. If those are facts, then, apparently, you have a battery with a capacity of 230Ah!

Are you sure that it’s a wet battery?

I have taken 23 Amps out of the battery leaving 77 Amps (100 AH Battery)
So! 90/77 x 100 = 116 ?

I suspect that you would need to discharge the battery to, at least, 50% in order to get an accurate estimate of the true capacity of your battery.

Hope that you had a nice evening celebrating with your family.

Ian

 

[John The Foot]

You have used 23Ah and your resting voltage after consuming 23Ah is 12.56V. Using the chart below, 12.56V represents a SoC of approximately 70%. Therefore, you have consumed 30% of the battery capacity. Since you have consumed 23Ah and this represents 30% of your capacity, you can now calculate that your true battery capacity is (23/30)*100 = 77Ah.

View attachment 868414

Ian

Makes me wonder how many people have a digital multimeter calibrated to 2 decimal places to accurately determine how good their batteries are.

 

[bigtwin]

Makes me wonder how many people have a digital multimeter calibrated to 2 decimal places to accurately determine how good their batteries are.

There are plenty of cheap DVMs available (for less than £20?). Given the importance of the electrical systems they are an invaluable part of one’s toolkit.

There is little need for calibration as most of the checks that you undertake are for indicative purposes only. You should also be aware that a resolution of 2 decimal places does not mean that it is accurate to 2 decimal places.

Finally, the battery capacity test is a rough guide to the health of the battery and is generally undertaken only when you suspect that the battery is on the way out (the test will not give an accurate assessment of capacity). I‘d be surprised if more than 0.1% of motorhomers have ever undertaken such a test.

Ian

 

[PhilandMena]

Ahh, yes, the wet lead chart shows 12.56V as only 10% discharged.

The error you made in your calculation below was assuming that your ’remaining’ 77Ah was a given when, in fact, that is the variable that you’re attempting to establish. The known facts are that you took 23Ah out of the battery and that, according to the wet chart represents a discharge of 23Ah. If those are facts, then, apparently, you have a battery with a capacity of 230Ah!

Are you sure that it’s a wet battery?



I suspect that you would need to discharge the battery to, at least, 50% in order to get an accurate estimate of the true capacity of your battery.

Hope that you had a nice evening celebrating with your family.

Ian

Hello again, Now recovered from last nights celebrations. (My grandaughters 18th Birthday bash). All of my figures are correct, apart from my calculation which I agree does not make sense. It was autorouter who gave me the process and calculations to establish remaining capacity and the only way I could make the maths give a meaningful result was to use a different formular. My post on this when I did the test was as follows.
Test is more or less finished but my maths do not make sense.
After resting the battery for one hour it measured 12.56 Volts. I have taken 23 Amps out of the battery leaving 77 Amps (100 AH Battery)
So! 90/77 x 100 = 116 ?
But if I do this 77/90 x 100 = 85.5 This would indicate I have used 14.5 % of my total battery capacity which I think makes sense !
Very happy with that, if it is correct ? I will measure again after two hours resting.

I never did get to the bottom of this and I will be the first to admit my maths is weak. The batteries were OK Excide ET650 wet cell lead acid 100AH. There were well supported in use by 245 W of Solar and I have a BM-1 battery monitor and they never were discharged below 60 % DOD with the average discharge around 75-80%. However, loads of cycles especialy when wilding in Morocco.
I trawled through the internet and looked at 12 V Lead Acid battery charging charts and there is a lot showing 12.9 which is for AGM and 12.7 the bog standard wet cell flooded. Some of the charts do not distinguish between the types so I can un derstand why some people may be misslead on this. Anyway, its all in the past as I now have Pure Carbon Lead AGM leisure batteries installed and 375W of S.P.

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[PhilandMena]

Makes me wonder how many people have a digital multimeter calibrated to 2 decimal places to accurately determine how good their batteries are.

I would have thought most if not all were made to some sort of agreed standard. Mine came from Aldi and cost around a tenner as best as I can recall.

 

[Steve and Denise]

Far too sensible for this thread.

Use a jubilee clip as cable ties melt if you pull high amps

 

[rrowe]

Use a jubilee clip as cable ties melt if you pull high amps

Our garage use a Bosch battery tester
That type in the model number of the battery and connect to the terminals
The readout displays all the numbers for the battery condition
Most importantly it shows the capacity so a 100ah battery that is well past it’s best may show 77ah which is what my Land Cruiser one did
It is then tells you what to do eg OK, charge the battery or replace
Cynics might suggest that the meter is tricked to always say replace battery!

 

[PhilandMena]

Our garage use a Bosch battery tester
That type in the model number of the battery and connect to the terminals
The readout displays all the numbers for the battery condition
Most importantly it shows the capacity so a 100ah battery that is well past it’s best may show 77ah which is what my Land Cruiser one did
It is then tells you what to do eg OK, charge the battery or replace
Cynics might suggest that the meter is tricked to always say replace battery!

I suspect this test is for a starter battery. (A Cold Cranking Test CCA) There are devices out there that can measure remaining capacity on Leisure batteries but they are very, very expensive.
A conventional "drop test" is not what is required.

Drop tests exert a very high discharge current across the battery for a short time and are meant for testing the CCA of engine starter batteries - not leisure batteries - which have a completely different discharge profile.
The test you need to determine the health of a leisure battery is a slow discharge test over 20+ hrs using a high resistance load. Drop testing a leisure battery repeatedly can do more damage than would be caused by completely flattening it.

And yes - if they allowed the battery to discharge completely they have almost certainly reduced its capacity to some extent.

 

[autorouter]

Makes me wonder how many people have a digital multimeter calibrated to 2 decimal places to accurately determine how good their batteries are.

I've tested many multimeters, expensive and cheap, against a certified calibrated voltage standard traceable to National Standards (NPL), and I've found they were all good for the first decimal place, and many to the second decimal place. I think I would trust any random multimeter over a motorhome voltage display, especially if two multimeters agreed with each other so I'd know there's no obvious fault.

The problem with voltage charts is that the voltage must be measured in very standardised circumstances - letting the battery 'rest' for at least an hour with no load or charging - which is difficult to do unless the battery is disconnected and on a bench in front of you. And even then I'm not very confident that the voltage reflects the state of charge accurately.

Having said that, I think most multimeters read high when the internal battery is getting very low, so that's always worth checking if the meter is new to you.

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[Jimbohorlicks]

Google Image Result for https://www.mobile-solarpower.com/uploads/1/2/9/6/12964626/published/msf4vpdl-1_14.jpg

From the attached chart your lifpo4 battery is fully charged thats why your charger wont charge it any further.
Also if your using an ordinary lead acid battery charger that you used for your duff batteries you have taken out it will "see" the 14.1 v as fully charged and won't put any more in.
There is nothing wrong with your new lithium battery. Just use it and use some of the charge.then recheck it.

 

[Stans Van]

Hi everyone

We recently converted to 1 x Lithium (LiPePO4 100ah), after being told our 2 x Bosch L5 013 90ah 800a batteries had had it and needed replacing. However, on connecting them to a charger, they show 14.1v and switch off, presumably because they both think they're fully charged

So, knowing nothing much at all about batteries, how do I know that they really have had it before I scrap them, please?

PS I don't mind if I've been hoodwinked into converting to Lithium. I just want to know that I'm not scrapping perfectly good batteries

Hi. Have smart shunt fitted…

 

[mohawkman]

I was lucky with my batteries since they were the removable caps on the cells and i used the old fashioned way with a hydrometer. After i could'nt find my old one and got one from Amazon next day. In both batteries no 6 cell wouldnt even float the damn thing. Mind you they were 8 years old and the others were borderline.

 

[PhilandMena]

Hi. Have smart shunt fitted…

I suspect the 14.1 V you were seeing was coming from the charger.

 

[HKF]

Hi. Have smart shunt fitted…

I'm sorry but I don't understand your post. What's a smart shuntand what does it do, please? And what does it fit to?

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[bigtwin]

I'm sorry but I don't understand your post. What's a smart shuntand what does it do, please? And what does it fit to?

A shunt is a device that measures current into/out of a battery. A smart shunt can accept information about the battery bank such as capacity, type, etc and can use that information to determine how much energy has been used and, hence, how much capacity remains available.
A really smart shunt will also have bluetooth capability such that you can obsess about your batteries status by viewing an App on your phone (or, in the absence of this, via a remote display).

Ian

 

[LithiumConvert]

I'm sorry but I don't understand your post. What's a smart shuntand what does it do, please? And what does it fit to?

Don't worry about it. They are just like smart motoways, smart TVs and smart alternators. Jack of all trades: Master of none.

Buy a good battery meter with its own wired display.

I have found the NDS Energy Meter from RoadPro to be an excellent piece of kit. Does what it says on the tin.

 

[HKF]

Don't worry about it. They are just like smart motoways, smart TVs and smart alternators. Jack of all trades: Master of none.

Buy a good battery meter with its own wired display.

I have found the NDS Energy Meter from RoadPro to be an excellent piece of kit. Does what it says on the tin.

Will this help me to see the drain over a period of time, please, so that I know if the batteries are done for?

EDIT - I've just seen the price of these. More expensive than one of my batteries

 

[chesterfield hooligan]

My head hurts.

 

[bigtwin]

Jack of all trades: Master of none.

Congratulations, you win the “Most sweeping (and unfounded) statement of the thread” prize.

Ian

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[bigtwin]

Buy a good battery meter with its own wired display.

I presume that you do realise that what you are describing is a smart shunt but one with a hardwired display?

I have found the NDS Energy Meter from RoadPro to be an excellent piece of kit. Does what it says on the tin.

It may be an excellent piece of kit but it isn’t really suitable if you run a medium/large inverter as it has a relatively low current rating.

Ian

 

[LithiumConvert]

I presume that you do realise that what you are describing is a smart shunt but one with a hardwired display?

It is just a shunt with a microprocessor display - nothing 'smart' about it. We have had shunts for decades; long before 'smart' became the latest sales gimmick.

 

[bigtwin]

EDIT - I've just seen the price of these. More expensive than one of my batteries

The Victron Smart Shunt is better, and cheaper, than the NDS item you've just looked at and is available from RogerIvy on here who also gives a Funster discount.

Ian

 

[autorouter]

It is just a shunt with a microprocessor display - nothing 'smart' about it. We have had shunts for decades; long before 'smart' became the latest sales gimmick.

Victron, who make the SmartShunt, seem to use the appellation 'Smart' to indicate that the device has Bluetooth communication built-in, and can communicate with all the other Victron Bluetooth-enabled devices. The SmartShunt doesn't have a wired display like their BMV range, so it's named to distinguish it from those.

 

[bigtwin]

It is just a shunt with a microprocessor display - nothing 'smart' about it. We have had shunts for decades; long before 'smart' became the latest sales gimmick.

Indeed, shunts have been around for donkeys years. Your shunt/display is ‘smart’ because it does more than just measure current, it has all the relevant parameters to calculate SoC for a particular battery type. It might not have bluetooth comms and be hardwired but it’s still ‘smart’.

Ian

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