Some battery questions

[booster]

Originally Posted by RossWilliams

"You have now added another term of "life cycle"

No I didn't add the term, the term "life cycles" is in the title of the graph you posted.

"Please show us where it says anything explicitly about defining a DOD of a cycle as 100%"

It is stated clearly at the bottom of the graph you posted. "DOD=100%"

"20AH times 2800 cycles = 56,000AH lifetime


80AH times 550 cycles = 44,000AH lifetime"

2800 cycles on 100ah battery will give you 280,000 Ah lifetime. But, in fact, battery AH ratings are based on how much power is provided when drawn down over a 20 hour period. If you draw it down faster or slower than that the amount of power provided will change.

"This is different than the traditional 50% rule that would make you believe that if you ever went below 50% the sky would fall."

I have not seen that going below 50% would damage the battery. I have seen that going below 20% for most AGM batteries can do permanent damage. Every description of the "50% rule" I have seen describes it as a suggested balance point between battery life and power needs.

What the graph shows is that a DOD of 80% average instead of a 50% average will cut the amount of power you get over the life of your battery by half. That assumes you monitor power very finely and never actually drop below 80%. In real life, no one could sustain an average DOD of 80% without damaging an AGM battery.

I am not going to rehash what has already been said, but the note the says DOD 100% refers to the full scale range of the testing. You could have similar charts that go to 80%, which would be more common in real world use. The big thing this would imply to me is that the chart is based on being totally full at the beginning of all tests, which is very critical a parameter. You were implying that the term life cycles somehow defined cycles as cumulative, which certainly doesn't appear too, IMO.



From the Lifeline FAQ section of Glossary

Cycle


One sequence of discharge and charge.


Cycle Life


The total number of charge/discharge cycles before the battery reaches end of life (generally 80% of rated capacity).

Based on this, and the fact that AGMs, including Lifelines, are typical advertised as having 1100 cycles at 50% discharge, I look at the chart and that is exactly what it says.



We are talking about Lifelines definition, their chart, their specs, and I can say I have seen anyone say that a life chart like this uses the full battery capacity to fine total energy over life.



If you have any reference for the definition of a cycle other than Apple that says otherwise, we need to see that information, or we just have to assume it doesn't exist. Yoshimuru appears to have been searching for it, but has not been able to find one.

[markopolo]

Using the posted Lifeline chart:

2750 cycles at 20% DoD
1050 cycles at 50% DoD
550 cycles at 80% DoD

If we assume that it is a 12V 100Ah battery then:
2750 * 20Ah * 12V = 660 lifetime kWh
1050 * 50Ah * 12V = 630 lifetime kWh
550 * 80Ah * 12V = 528 lifetime kWh

If comparing 50% vs 80% DoD life using cycles then it looks like you'd lose 50% of the battery's life.
If comparing 50% vs 80% DoD life using kWh then it looks like you'd only lose 16% of the battery's capacity life.

You can choose to see battery life in terms of cycles or kWh or even both.

[Yoshimura]

Maybe someone should ask Lifeline their definition of a cycle?

[RossWilliams]

"We are talking about Lifelines definition, their chart, there specs,"

But apparently not their conclusion that it makes a "dramatic" difference in battery life?

"Based on this, and the fact that AGMs, including Lifelines, are typical advertised as having 1100 cycles at 50% discharge"

The chart actually shows about 1000 at 50% discharge. You are assuming they are using a definition of cycle that meets your conclusion that there isn't a significant difference, but contradicts theirs that there is.


Try Google "battery cycle full discharge":

"May 18, 2017 - A discharge/charge cycle is commonly understood as the full discharge of a charged battery with subsequent recharge, but this is not always the case. Batteries are seldom fully discharged, and manufacturers often use the 80 percent depth-of-discharge (DoD) formula to rate a battery." https://batteryuniversity.com/learn/...charge_methods


Note the "commonly understood" portion of that.

There are several other similar links on Google. Including this one :

"A charge cycle is a complete charge and discharge on a rechargeable battery. ...

A charge cycle can be a complete full charge to discharge or a series of partial drains adding up to the battery’s capacity. "

https://whatis.techtarget.com/definition/charge-cycle

[RossWilliams]

"If comparing 50% vs 80% DoD life using cycles then it looks like you'd lose 50% of the battery's life.
If comparing 50% vs 80% DoD life using kWh then it looks like you'd only lose 16% of the battery's capacity life."

Which would make cycles meaningless unless you are claiming that every time you recharge a battery you have used up a full cycle. Do you have to fully recharge it, or is a partial charge a full cycle as well? If you never fully recharge it, do you never use any cycles?

Cycles are a meaningful measure of battery life only if you accept the generally understood definition of battery cycle as 100% discharge and 100% recharge no matter the amount of individual discharges and charges.

TO be clear. the graph above is not comparing 50% cycles at 50% DOD to 80% cycles at 80% DOD. It is comparing 100% cycles at 50% DOD to 100% cycles at 80% DOD. It illustrates the "dramatic" difference in battery life from shallower discharge cycles.

[markopolo]

For a moment there I thought you were onboard Ross!


IEC - IEC 60050 - International Electrotechnical Vocabulary - Details for IEV number 482-05-28: "cycling (of a cell or battery)" - defines cycling as

cycling (of a cell or battery) - set of operations that is carried out on a secondary cell or battery and is repeated regularly in the same sequence

Note – In a secondary battery these operations may consist of a sequence of a discharge followed by a charge or a charge followed by a discharge under specified conditions. This sequence may include rest periods.

secondary cell - cell which is designed to be electrically recharged

primary cell - cell which is not designed to be electrically recharged



I came across this interesting report on a particular IEC test from Trojan Battery: https://www.trojanbattery.com/pdf/27-AGM_IEC-61427.pdf It's not exactly related to the current trend of this topic but the projected 8 1/2 year expected life of the battery whilst subject to partial state of charge (PSOC) cycling (both LSOC & HSOC) is encouraging.

[markopolo]

Originally Posted by RossWilliams

.....................Cycles are a meaningful measure of battery life only if you accept the generally understood definition of battery cycle as 100% discharge and 100% recharge no matter the amount of individual discharges and charges.............

Explain how these 100% discharge and 100% recharge equivalent cycles can be used if it is a meaningful measure of battery life. Can you compare your 100% discharge and 100% recharge equivalent cycles to a battery life expectancy chart somewhere? Is that how your lead acid battery is warrantied (like Apple batteries)? I don't see how 100% discharge and 100% recharge equivalent cycle data can be used. kWh, on the other-hand is useful data. Maybe if I knew how you use the data it would help me understand why you think it is useful.

[RossWilliams]

One more:

Deep Cycle Battery FAQ

"Battery Cycles vs. Battery Lifetime?

Often the lifespan you can expect to get out of your battery is referred to in terms of "cycles". A battery cycle is one complete discharge and recharge cycle. The discharge state of a battery is often measured in Depth of Discharge (DOD). This refers to how far down the battery has been taken, for instance, a battery that has 25% of its capacity remaining would be said to be at 75% DOD. The lifetime of a battery is directly related to the depth of the discharge that it regularly experiences. Lead acid batteries are fickle things. If you subject a deep cycle battery to 80% DOD on a regular basis you will get roughly half the life out of your battery than if you were to cycle it to 50% DOD. While this doesn't mean that you can't go down to 80% DOD you should generally try to design your battery banks to allow for cycling at around 50%. Conversely there is also an upper limit on the DOD of a battery, usually, a battery that is only regularly cycled down to 5% or less will not last as long as a battery cycled to 10% or more. This is because on smaller cycles the Lead Dioxide can clump up around the positive plates. On heavier discharges, this would be more of an even film."

[RossWilliams]

"Explain how these 100% discharge and 100% recharge equivalent cycles can be used if it is a meaningful measure of battery life."

I already did. If you look at how many KW you will get over the life of a battery you can see pretty clearly that you get more KW the more cycles you have and you get more cycles the shallower your DOD. The difference is dramatic if you use the common definition of battery cycle, discharging to 80% DOD and recharging uses .8 battery cycles, to 50% DOD and recharging uses .5 battery cycles. But the total number of those battery cycles you get is much greater at 50%.

[markopolo]

You don't need your 100% discharge and 100% recharge equivalent cycle theory to come to that conclusion. You can just look at any battery manufacturers chart to see that.

I'll rephrase - is there any unique information or usefulness that is derived from the 100% discharge and 100% recharge equivalent cycles theory?

[RossWilliams]

"You don't need your 100% discharge and 100% recharge equivalent cycle theory to come to that conclusion. "

If you accept the idea that a discharge to 80% DOD only uses .8 cycles, then I guess we agree. But the usefulness of measuring using full discharge and recharge cycles is that you have a common measure of energy produced by a cycle. It shows the dramatic impact of lower DOD's on total energy produced over the life of the battery without confusing it with the amount of energy you get from a partial discharge.

There is a big difference between the idea that you can charge and discharge a battery 1000 times to 50% DOD and that you can discharge a battery to 50% DOD the equivalent of 1000 full discharges. In fact, the latter results in twice as much total power. The difference is even larger using 20% DOD, where you are talking about 5 times as much power using full discharge cycles.

[booster]

I think we need to do some common sense logic here.


Take the highest number of cycles from Apple at 1000 cycles. At 20% discharge you would get to recharge your device 5000 times by their definition of cycle.


Now look at the Lifeline AGM that shows 2800 cycles at 20% discharge, so they would get 14,000 recharges if the battery use the adding up theory.


At 80% discharge the Apple would get 1250 cycles.


At 80% discharge the Lifeline would show 550 cycles and get 687 recharges.


Does anyone really believe that the AGM battery is going to last 2.8 times longer than the lithium at 20% discharge depth, but the lithium is going to last 1.8 times longer at 80% discharge?


Now take a look at AGM using the non Apple cycle definition.


At 20% discharge the AGM will get 2800 cycles and the lithium will get 5000, so the lithium will last 1.8 times longer.


At 80% discharge, the AGM will get 550 recharges and the lithium will get 1250, so the lithium will last 2.27 times longer.


They tout lithium batteries last a longer than AGMs, particularly at deeper discharges.


Which calculation actually make sense?

[booster]

OK, here we go. I found this technical paper.


https://www.researchgate.net/publica...Acid_Batteries


While they do mention cycles both ways for various test modes, the important thing is the results, which are summarized in a chart the shows total lifetime energy out, and also shows "cycles" vs DOD.





This shows the cycles vs DOD very similar to the Lifeline chart. The total energy in and out is nearly constant, as we have been saying.


This plainly shows that you don't get double the lifetime energy at 50% compared to 80%.

[booster]

I found a specifically explained definition of "cycle" on the Rolls battery site in this tech manual.


http://www.rollsbattery.com/wp-conte...ery_Manual.pdf


Hear is what probably the premier battery manufacturer of deep cycle batteries has to say.




I think this explains it all very well, and from a very respected source.

[Yoshimura]

When I was exposed for the first time to these "Cycles vs DoD" graphs, my initial understanding was that the number of cycles represented the number of times I could use the battery (or more precisely how many times I could discharge it to a particular DoD). From that, it became obvious that I had to limit the depth of discharge if I wanted to be able to use the battery longer (or more times). And even if I was correctly interpreting (IMO) the meaning of a cycle, the penalty for deeply discharging a battery seemed very steep. However, when you take into account that every time you discharge it deeply, it also means that you used it more, it become obvious that the penalty is in fact small.

So this is my reasoning.

[Yoshimura]

Originally Posted by RossWilliams

I have not seen any reference that treats a cycle as a anything other than a fixed depth of discharge, usually 100%. Cycle life however is not fixed, as the chart shows. At an average depth of discharge of 25% you will get roughly 2000 cycles, at 50% you will get 1000 cycles and at 80% you will get roughly 500 cycles.

If you have three battery banks, one of 1200 watts, one of 2400 watts and one of 4800 watts and each one uses 1200 watts of power per day and then recharges. The 4800 watt bank discharges to 25% the 2400 watt to 50% and the 1200 watt to 80%, requiring at least one recharge during the day. Here is what happens over the life of the battery.

4800*2000 = 9600000 watts 8000 days/1200 watts per day
2400*1000 = 2400000 watts 2000 days/1200 watts per day
1200*500 = 600000 watts 500 days/1200 watts per day

...

Ross, I not sure I follow you here...

If a cycle is defined as a complete battery discharge (either in one or multiple shots) this mean that every time you discharge the battery to 25% DoD, you are in fact using 1/4 of a cycle, right?

If at an average depth of discharge of 25% you will get roughly 2000 cycles, this mean that you could use the battery 8000 times, right?

Are you aware that 8000 times is like 22 years (when used once a day)?

[booster]

Originally Posted by Yoshimura

When I was exposed for the first time to these "Cycles vs DoD" graphs, my initial understanding was that the number of cycles represented the number of times I could use the battery (or more precisely how many times I could discharge it to a particular DoD). From that, it became obvious that I had to limit the depth of discharge if I wanted to be able to use the battery longer (or more times). And even if I was correctly interpreting (IMO) the meaning of a cycle, the penalty for deeply discharging a battery seemed very steep. However, when you take into account that every time you discharge it deeply, it also means that you used it more, it become obvious that the penalty is in fact small.

So this is my reasoning.

IMO, your reasoning is spot on, and is what some us have been saying for a while now. The charts have been badly misinterpreted, IMO, perhaps in an effort to sell folks more batteries than they need. If you look back at the link to the older discussions there is a total energy chart done for the Lifeline AGMs that shows just how much you would actually lose in the areas below 50% (if you went there all the time)



I think very, very, many of us hover in the 30-50% discharge areas almost all the time, I know we do probably 98% of the time. But many or most of those same folks will occasionally need to go beyond 50% DOD, and some of the 50% rule folks claim that for the 2% of the time they would need that bit of extra capacity, they should add more batteries or they will destroy the smaller ones all the time. It appears from all we have found out that going below 50% is a minor (21% loss of total energy per your calcs) loss, and that is if you do it on every cycle. Doing it on 2-5% of the cycles won't ever be noticed in the life of the batteries, IMO.


Even if you did do 80% DOD all the time, many of us would gladly buy batteries a bit more often to prevent the cost, weight, space issues with adding more battery capacity. IMO, the biggest reason you would need to add more batteries would be to run large load items like microwaves or cooktops, as you need more battery capacity to hold the voltage up to prevent low voltage cutout of the inverter.


Instead of spending money on more batteries, I think you would get more bang for the buck out of spending the money on top line charging equipment, for shore, solar, and engine. AFAIK, there are only a small handful of folks on this forum that have the ability to charge very accurately to full charge, and only a fraction of those folks can do it without operator intervention. Getting to a confirmed 100% state of charge, based on charging amps to the batteries, every 7-10 charge cycles is probably the single best way to improve battery life and capacity preservation.

[booster]

This is just for reference from the other discussion. These charts were calculated the same was as the tech paper on shown earlier for total lifetime energy of a battery.














None of the lead acid batteries show anywhere near double total energy at 50% compared to 80% DOD. The lithium battery curve is a bit suspect as at the time there was very little information available and the source was said to be very conservative in rating.

[markopolo]

As Booster has pointed out, occasionally going to 80% DoD shouldn't be problem at all and extra money is likely more wisely spent on better charging equipment and monitoring. If routinely going to 80% DoD is unavoidable and installing additional batteries is not an option then you'll probably lose up to 20% of the batteries lifetime output capacity and have to replace it earlier.

The cycle charts from battery manufacturers just don't match up with RV type use. We don't discharge and charge the battery the same amount everyday.

It is really important to fully charge the battery after use. Temperature compensated charging by Ending Amps is the best way to do it IMO.

[booster]

Originally Posted by markopolo

The cycle charts from battery manufacturers just don't match up with RV type use. We don't discharge and charge the battery the same amount everyday.

It is really important to fully charge the battery after use. Temperature compensated charging by Ending Amps is the best way to do it IMO.

I think this sums it up well.


The highlighted red, as has been mentioned elsewhere also, is probably the single best way to maintain battery capacity and improve life. The full charge doesn't have to happen on every cycle, but most manufacturers I talked to said at least every 7-10 cycles when you are cycling them often, but no more than two weeks if not cycling often regardless of number of cycles.



Very, very, few people have the charging equipment that can actually do this kind of charging, so they are almost certainly over or under charging essentially all the time, IMO.