Are all battery Ah created equal?

T1 Terry · Guru

Are all battery Ah created equal?

Mr Fuse · Veteran Member

I realise a lot has changed since I first learned this stuff some 50 odd years ago, and this may well be one of those things, but at that time the Ah rate for lead/acid batteries was the 20 hour charge time from flat, at 25 degrees C ambient, not the discharge time. The temperature is quite an important ingredient if you hope to have any sort of reliable reference. Why charge time rather than discharge time? because then you measure what the battery will hold, rather than what it might deliver.

markf · Senior Member

Mr Fuse wrote:
I realise a lot has changed since I first learned this stuff some 50 odd years ago, and this may well be one of those things, but at that time the Ah rate for lead/acid batteries was the 20 hour charge time from flat, at 25 degrees C ambient, not the discharge time. The temperature is quite an important ingredient if you hope to have any sort of reliable reference. Why charge time rather than discharge time? because then you measure what the battery will hold, rather than what it might deliver.

Many moons ago when computer room UPS's were full of BIG wet cells and computer room temps were kept at around 20 deg C the doco that came with the cells always specified "Charge Capacity" and "Discharge Capacity" @C2 and @20 deg C. The manufacturers always went to great pains to emphasise that these numbers were a guide only. The meaning behind the numbers was as important as the numbers themselves. The discharge capacity was mostly about how long the batteries in the UPS would last until either the mains came back or the generator started. The charge capacity was about how long the battery would take to charge from dead flat (usually 1.5V / cell). They were usually two wildly different numbers. An example that I can remember for a single cell is Discharge Capacity 320Ah with a Charge Capacity of 800Ah. I haven't seen these numbers published by any manufacturer for decades though.

It'd be nice, but unlikely, if all manufacturers of all battery types could publish a single number to enable easy comparison. Maybe measure Ah from full charge to flat at C20. Maybe a meaningless number in itself but useful for comparison. This'd mean that a 100Ah chemistry X battery would be comparable to a 100Ah chemistry B battery.

-- Edited by markf on Friday 19th of July 2019 11:31:08 AM

Mr Fuse · Veteran Member

All the UPS batteries I've seen for at least the last 20 years or so, which have all been gel cells, have an Ah rating without providing the any clear and relevant details about that rating. These days I prefer to simply measure the run time and disregard anything on the batteries. After all, that's the only value of relevance. Not having a generator we rely on that run time figure to determine if and when to starting shutting systems down. That's less important at home, because I do have a generator. But of course my home UPS loads are minuscule in comparison.

T1 Terry · Guru

The only problem with that idea is that lead acid batteries never stop accepting charge current. Any cell that has current passing through it in either direction is also an electrolyser separating water into hydrogen and oxygen and a heater due to the internal resistance involved in the chemical reaction involved changing lead sulphate into lead and water into sulphuric acid, and the same when discharging. This is all wasted energy, electrical energy that did not directly translate into stored battery capacity.

It takes 125% of the advertised capacity of any type lead acid battery to bring it from fully discharged to fully charged. Fully discharged is not 0V by the way, fully discharged is all the cells at their manufacturers accepted minimum voltage

Full River battery puts out this chart

Fullriver DC105ah AGM.JPG

The C20 curve shown as a 5.25 amp discharge for 20 hrs stops at 10.5v divided by 6 cells = 1.75v. It is assumed this voltage is under load because the end of discharge voltage for higher discharge rates becomes lower and lower, the C1 discharge rate (105 amps from a 105Ah battery) ends at 9.5v, divided by 6 = 1.58v per cell. At a 3C rate (315 amps) the end voltage is 9v or 1.5v per cell. If you dragged the battery down to that voltage with a 5.25 amp load you would have caused serious damage, if you dragged it that low the resting voltage was 1.5v per cell, it will not return to 100% capacity no matter how hard you try because the lead plates will have shed material as a result of such a seriously low voltage discharge.

This is the recharge charts https://resources.fullriverbattery.com/fullriver-battery/external-media/manuals/charging-instructions.pdf if the reader can follow that then they already fully understand what I'm talking about, but then they wouldn't be reading this stuff in the first place eh :lol:

Directly under the Charging Instructions heading on the right is a chart shows the type of charging we all use, voltage controlled or regulated as they call it. Note the float charge minimum time, you are never going to achieve that using solar so you are never going to get the battery fully recharged to 100% SOC recharging with solar, so charts showing a discharge from 100% SOC to what ever and how many cycles you can expect do not relate to lead acid batteries recharged by solar only.

Also note the absorption voltage 2.45v x 6 cells = 14.7v =/- 0.15v, and the max time, 8 hrs. Are you ever going to get enough sun to get the battery up to 14.7v and then hold it at that voltage for 8 hrs? Something to think about when programing your solar regulators. Basically as I read it, float voltage is only for batteries that are not presently in cyclic use, in other words at home with everything turned off but the solar still running or connected to a mains charger.

T1 Terry

T1 Terry · Guru

markf wrote:
Mr Fuse wrote:
I realise a lot has changed since I first learned this stuff some 50 odd years ago, and this may well be one of those things, but at that time the Ah rate for lead/acid batteries was the 20 hour charge time from flat, at 25 degrees C ambient, not the discharge time. The temperature is quite an important ingredient if you hope to have any sort of reliable reference. Why charge time rather than discharge time? because then you measure what the battery will hold, rather than what it might deliver.
Many moons ago when computer room UPS's were full of BIG wet cells and computer room temps were kept at around 20 deg C the doco that came with the cells always specified "Charge Capacity" and "Discharge Capacity" @C2 and @20 deg C. The manufacturers always went to great pains to emphasise that these numbers were a guide only. The meaning behind the numbers was as important as the numbers themselves. The discharge capacity was mostly about how long the batteries in the UPS would last until either the mains came back or the generator started. The charge capacity was about how long the battery would take to charge from dead flat (usually 1.5V / cell). They were usually two wildly different numbers. An example that I can remember for a single cell is Discharge Capacity 320Ah with a Charge Capacity of 800Ah. I haven't seen these numbers published by any manufacturer for decades though.
It'd be nice, but unlikely, if all manufacturers of all battery types could publish a single number to enable easy comparison. Maybe measure Ah from full charge to flat at C20. Maybe a meaningless number in itself but useful for comparison. This'd mean that a 100Ah chemistry X battery would be comparable to a 100Ah chemistry B battery.

-- Edited by markf on Friday 19th of July 2019 11:31:08 AM

That was the reason I mentioned I would do a recorded C20 discharge on a C2 rated 100Ah lithium battery, to get an apples to apples comparison.

My real concern is the misleading statements made by many, including battery manufacturers, about the capacity in Ah their battery has stored. If the C rate the discharge was conducted at isn't clearly stated, the number is meaningless. It is also meaning less comparing a battery rated at a C20 or C100 discharge rate with a battery discharged at a C2 rate by the advertised Ah capacity.

The fact that amps x volts equals power supplied in watts so amps used over an hour represents Ah is correct, as long as the voltage remains the same then the watt hrs will also be the same. That part remains as a basic building block for calculating just how much stored energy you use or need, it is the way the manufacturer presents that stored energy number (number of Ah) that needs to be clarified, then a real calculation of the stored required can be made.

T1 Terry

markf · Senior Member

Mr Fuse wrote:
All the UPS batteries I've seen for at least the last 20 years or so, which have all been gel cells, have an Ah rating without providing the any clear and relevant details about that rating. These days I prefer to simply measure the run time and disregard anything on the batteries. After all, that's the only value of relevance. Not having a generator we rely on that run time figure to determine if and when to starting shutting systems down. That's less important at home, because I do have a generator. But of course my home UPS loads are minuscule in comparison.

This was back in the 1970's. The UPS that I can most remember was for a large computer room full of IBM and Honeywell mainframes and the associated air conditioning and lighting. There was nothing smart about the UPS either - the generator had 15 minutes to get started and up to speed before the UPS just dropped all power because the batteries were below their threshold voltage and not because of a timer. The processing that was done in that computer room could probably be done on a phone today... smile

-- Edited by markf on Friday 19th of July 2019 12:35:32 PM

Mr Fuse · Veteran Member

Terry, I agree fully that the information needs to be, but isn't, presented it a consistent manner. These days, for automotive use at least, I apply the same principle as I do with UPSs - I use the Ah rating as a very course first approximation of suitability but I work out how long my load will run on the batteries I have and use that figure alone for the real world.The idealised charging chart you presented is a good example. Our camper can, with appropriate input supply, come acceptable close to those specs. On the other hand, the car will not do so. Therefore, the deep cycle batteries I will be installing in the car (which co-incidentally are FullRiver) will never be able to perform quite as well or last quite as long as the camper batteries. I know and understand this. Unfortunately a lot of people won't and may therefore become disappointed with their battery performance long term because all they have to go by are those numbers on the battery.

Noelpolar · Veteran Member

Mmm ..... maybe my 90ah Winston running my car fridge will be like 140ah at its 0.04C draw (and only when the compressor is running).

So... if only drawing 0.04C.... should my SOC monitoring be set to 80% of a 90ah or 140ah.....

T1 Terry · Guru

Noelpolar wrote:
Mmm ..... maybe my 90ah Winston running my car fridge will be like 140ah at its 0.04C draw (and only when the compressor is running).

So... if only drawing 0.04C.... should my SOC monitoring be set to 80% of a 90ah or 140ah.....

If it is a Victron 700 or 712 BMV, set the warning to 20%SOC and the relay to 5% SOC. Set the Peukert to 1.00 and the charge efficiency to 100%. Set the warning low voltage to 12.2v and relay to 11.8v, that way if the SOC goes out of wack the low voltage will save the battery from damage.

The ah in and ah out of a quality lithium are what you see is what you get, no losses either charging or discharging at the rate used for an RV house battery. You would get more ahs at a lower draw that the rated C2 before the voltage drops, but using the 100% of the battery capacity is the safest method and only relying on the voltage in an emergency where recharging isn't possible. If you can monitor the cell voltages then a lot more can be drawn at a low discharge rate until a cell drops to 2.8v under load, handy for that emergency spare bit but too much hassle watching cell voltages and worrying about going too low to be worth the effort normally.

T1 Terry

T1 Terry · Guru

OK. I finally have a bit of free time to do this comparison test between AGM batteries and lithium batteries at the recommended AGM capacity testing rate of C20 or discharged from fully charged to fully discharged over a 20hr period. Each battery type will then be fully recharged at the same rate so a comparison of time and total out v in can be made.
I've been saying that 100ah of quality lithium is equal to 200Ah of AGM batteries and this has been disputed by some members as not being an accurate comparison.
I have 2 x 100Ah Remco AGM batteries with maybe 3 mths use that were replaced with lithium batteries and the owner has given me the ok to use them for the test.
If I connect them positive to positive, negative to negative, the positive load/charging cables to one battery and the negative load/charging cables to the other battery, does this sound acceptable to the members as a suitable 200Ah battery configuration to do the comparative testing against a 4 x 100Ah Winston Batteries cell 12v battery, 3v x 4 cells in series to give 12v @ 100Ah?

Will the use of a Junsi cell logger and a Victron 700 BMV set to a Peukert value of 1 and charge efficiency of 100% be suitable for recording the battery voltages and total Ah out as well as total Ah in to recharge? The Junsi will also show each cell voltage of the 100Ah lithium battery throughout the tests, but unfortunately I can't access the cell voltages of the 2 AGM batteries without destroying the cases.

Does this sound like a suitable set up to do a comparison between the 2 chemistry batteries? I don't want to hear whinging that the test wasn't a fair comparison from either camp, so have your say now ......

T1 Terry

Aus-Kiwi · Guru

I know the debate on which battery is best is the Ford - GM thing ., What I have found if you have enough solar and battery storage ? With quality regular. Ive had no issues with AGM . Saying that if I fitted half ( or close to) the AH with Lithium batteries. I save on weight . What I have found since near doubling battery storage and tripling solar . Converting everything over to 12v. Except Microwave, electric jug which are used infrequently 2 or 3 times a day using inbuilt 5000w diesel generator day time . I have no problems running 220l fridge freezer and 50l portable fridge . Even during the last overcast days the voltage gets to 12.7 in the morning . Buy 10am its over 14v . On minimal charge, green light flashing . Comparing to our first system with 4 X 6v batteries , 180w solar . To now over 400 watt solar and 300+ AH storage . Plus VSR to motor batteries . We dont have any issues ., I think if your using too much battery ? Your system isnt large enough .? Most van manufacturers fit JUST enough . For lights and TV . Edit . Off subject a little . Ive had the same with solar on our home . First we fitted 5kw our power bill hardly dropped . We then fitted another 6.kw single phase system on 3phase system . Now our power is nearly neutral through winter, in credit through summer . In 18 months its paid for itself .

-- Edited by Aus-Kiwi on Saturday 31st of August 2019 01:23:25 PM

T1 Terry · Guru

Thanks Graeme, I'll give it a week for those who wish to comment regarding their views on the testing parameters as to whether they would be a fair comparison. It will be interesting to see just how many Ah can be drawn for the Winston 100Ah 12v battery before the battery voltage drops to 10v or a cell drops to the 2.5v mark while under the same 10 amp load as the 2 x 100Ah Remco AGM batteries. Winston rate the 100Ah capacity at a 50 amp load, so at only 10 amps I expect it will provide a lot more than 100Ah. What will also be interesting is how many Ah (while still under load) before the 11.8v mark is reached in each battery type as that seems to be the commonly excepted lower limit for deep cycle battery discharging without causing battery damage.

T1 Terry

Jaahn · Guru

Hi Terry smile

Sounds like a fair test. It will be interesting to see the results. What method do you have to provide the 10A load. It may need to be adjusted to compensate for the change in voltage over the time period of the test.

Jaahn

T1 Terry · Guru

I had a reread of the proposed testing and I realised the C20 test of 10 amps on the 2 x 100Ah AGM batteries would be a C10 test on the 100Ah lithium battery. To do the same C20 test on both batteries it would require a 10 amp load on the 2 x 100Ah AGM batteries but only a 5 amp load on the 100Ah lithium battery.
Should I reduce the AGM to a single 100Ah battery with a C20 load of 5 amps so the load would be the same for the 100Ah lithium battery? 5 amps is a very small load and doesn't truly represent the loads expected in even the most frugally powered RV, a single 60w car light bulb or halogen down light draws 60 watts and that equals 5 amps @ 12v.

The 10 amp test would be interesting at the 11.8v mark where most sensible people stop draining their battery to save its life and logic says they should both occur after 10 hrs @ a 10amp load, the 200Ah AGM discharged to 50% SOC and the lithium to 0% SOC, but the continued discharge to 10v on the 2 x 100Ah AGM batteries and 2.5v in any one cell on the lithium battery would show just how much would be left in the "tank" in the lithium battery at a lower discharge rate than the 50 amps the lithium battery's 100Ah was measured.
A conundrum, it wouldn't be an apples v apples test but would the reader recognise that the lithium battery was under twice the load of the AGM battery because the lithium battery was half the capacity of the 2 AGM batteries? I doubt the 100Ah lithium battery will last the 20 hrs under a C10 load, but again, maybe the AGM's won't either, I could be a real eye opener for all eh :lol:
I wonder what the knockers will say if the lithium battery does last as long as the AGM batteries at a relatively twice the load?

T1 Terry

Jaahn · Guru

Hi Terry smile

My opinion. You have said that 100ahr lithium is roughly equal to 200ahr AGM and a 10amp load is a reasonable test of what might be a normal load. That sounds OK to me so just do that for both. We know that the discharge is not the same Cx rate but normal buyers do not worry about that, they just want to know what the two battery types will do to power their normal load.

IMHO you should show the point at which the AGMs are 50% discharged, as people regard that as a important point. But you should continue to the end too for the full ahr reading.

Jaahn

-- Edited by Jaahn on Wednesday 4th of September 2019 07:44:18 AM

T1 Terry · Guru

I'm assuming half way between fully charged and the 10v under load end of test would be a definite 50% SOC point. What might be interesting is whether the 11.8v mark corresponds with the 50% SOC point mid way through the test.
This whole test is in answer to Peter'n'Margaret claiming an Ah is an Ah thegreynomads.activeboard.com/t65713167/advice-new-agm-battery/ He claims that the low current draw from an AGM battery if repeated on a lithium battery, that only 400Ah of lithium could replace 400Ah of AGM. The low current draw he refers to I'm guessing is the C20 rate or less, so comparing that against a C10 rate for the lithium battery isn't the same is it?
Many be the 100Ah of AGM v 100Ah of Winston LYP lithium should be the first test, at least that will show that from fully charged to fully discharged if the chemistries are the same as Peter claims or not, therefore Ah's are not all created equal when it comes to how a battery is advertised regarding its capacity.

T1 Terry

El Gringo · Senior Member

I would be interested to see how repeatable your tests are also.
IIRC it was mentioned that fully discharging an AGM or any LA battery doesn't hurt them?
This seems to go against the common conception of the chemistry.
So if you fully discharge these 2 different types of batteries and re-charge them, has there been any noticeable drop in capacity?
Of course time would be an issue, but doing multiple tests might show whether this is a myth or not...

Cheers,

T1 Terry · Guru

El Gringo wrote:
I would be interested to see how repeatable your tests are also.
IIRC it was mentioned that fully discharging an AGM or any LA battery doesn't hurt them?
This seems to go against the common conception of the chemistry.
So if you fully discharge these 2 different types of batteries and re-charge them, has there been any noticeable drop in capacity?
Of course time would be an issue, but doing multiple tests might show whether this is a myth or not...

Cheers,

The AGM 100% discharge chart for good quality batteries actually shows an improvement for the first lot of cycles before the cycle life starts to drop. Lithium batteries actually like being fully cycles every so often and a slow recharge (C20 or 5 amps per 100Ah) would probably result in their capacity increasing rather than reducing. I liken it to getting the air bubbles out of a waterbed, the steady discharge and recharge tends to improve the saturation of the cell material.

It will be interesting that's for sure. Might look into doing a video of the whole event and then speeding it up to lasting a minute, 20 hrs could be a bit of a stretch to hold the viewers attention :lol:

T1 Terry

Jaahn · Guru

Hi Terry smile

It is your test and you can decide to do what you like. However there could be several interesting tests to do. Your time and your batteries biggrin You choose.

As I said above I think the most interesting comparison for me would be the Lit 100ahr and the AGM 2x100ahr discharged at 10amp continued on to your end voltages for each. This would be a common basic setup for a lot of people.

You might like to test Peters statement about the low discharge rate giving a similar Ahr for both the Lit 100 and the AGM 100 at say 5 A. Valid test and interesting also. The AGM discharge time should be similar to the other test.
There may be more interesting comparison tests that others may like but they are not saying at the moment. disbelief

Jaahn

PS "Might look into doing a video of the whole event and then speeding it up to lasting a minute, 20 hrs could be a bit of a stretch to hold the viewers attention :lol: "

Yes well even a minute of some utube videos can be painfull !! so keep it short !

-- Edited by Jaahn on Thursday 5th of September 2019 11:58:31 AM

-- Edited by Jaahn on Thursday 5th of September 2019 11:59:08 AM

T1 Terry · Guru

Agree about the boring videos, even a 30 second ad can be 25 secs too long. Maybe one of those half screen things with me talking about what the test and showing the actual set ups that the other half screen was showing the speeded up readings of load amps, voltage, SOC and Ah passed through, all from the beginning to end of the test for each battery chemistry. That probably means I'll have to do the tests simultaneously, I have no idea about videos, how things are put together or even how you post a video on You Tube, so that will be all in someone else's hands.

T1 Terry

T1 Terry · Guru

Resurrect this from the 2nd or 3rd page. The battery I had built for the experiment ended up in a customers van, probably our first ever drop in customer thanks to a referral from the manager at Blanchetown caravan park. Then work got in the way with a project to converter a house boat to electric propulsion as well as full electric for the house power.

Anyway, I have built another battery, well 4 actually because there are other videos we want to make regarding the difference between 4 x 100Ah lithium batteries and a 400Ah lithium battery, but that's for a later topic

I have had 2 x 100Ah Bosch Gel batteries on the charger @ 13.8v for 10 days (240hrs) and the charge rate has remained constant for the last few days at 0.10 amps for one battery and 0.21amps for the other battery. This indicates this is the self discharge rate of each battery and they have accepted all they are going to take. Next step is to test discharge each battery to see if it has 100Ah @ the C20 rate (5 amp discharge) before it hits the 10v mark under load. Not much point in trying to compare a battery that didn't start out with 100Ah capacity eh :lol: Still waiting to see if the owner of the 2 x 100Ah Remco batteries wants to get them back for his next 4 x 4 motorhome he plans to buy or if he is keeping the Avida. Seem to change day to day some times
If these Bosch batteries aren't up to the task I'll just go back to the Remco batteries and hope the test doesn't get interrupted half way through.
I'll set the Junsi logger to 5 min sampling, 20 per hr and 400 if the battery holds out for the full 20 hrs while still maintaining 10v under load. I'll use the Junsi as the load cut off if the voltage drops below 10v with a timer set to 1 hr off so the recovery will be easy to see and the effect of the load when it resumes. I'll also use a Victron 700BMV to monitor the battery so the total Ah out can be recorded.
we are still working on a method of recording the instant information flow from multiple Victron BMV units so we can post them as a graph the same as the Junsi provides. That will be good for side by side comparisons between batteries for all sorts of different tests.

T1 Terry

T1 Terry · Guru

A slight review on the sample timing of the Junsi logger, it appears as though 2 mins is the longest interval span available, so a lot more plot points. It won't really matter, just a more precise graph, just a bit longer that's all.
The first battery is on test now. Charged to 14.4v, off charge to rest for 1 min, then the 5 amp load switched on. First thing I noticed, there is capacity available above the 12.8v mark that is accepted as fully charged, it held above the 12.8v mark while under a 5 amp load for a few mins so that bit between 12.8v and 13.8v is more than just a surface charge, it does have some capacity even if a 5 load only represents 0.08Ah per min.
We will see what the graph says in 20 hrs time .... no, I won't be sitting watching :lol:

T1 Terry

T1 Terry · Guru

Learnt a few things today, even though the Victron said there was still 58% SOC remaining, the battery had apparently hit the 10v mark because the load was off. The Victron showed 41Ah had been extracted and the voltage had bounced back to 11.38v. Rather than end the test there, I turned the Projecta IC5000 charger on set to power supply mode so up to 50 amps could flow into the battery but the voltage couldn't go above 13.8v. It took roughly 1 min at 50 amps to go from 11.11.38v to 13.8v before the current started cycling back, but it seems to be holding at 30 amp at the moment. It shouldn't take long to put 41Ah back in at even 30 amps so I'll shift it up to the Gel setting once the amps drop to around 10 amps.
Hopefully the Junsi logger has recorded it all so I can share the graph with you.

T1 Terry