" so at 20% per your explanation, you should get 2200 cycles"
Uh no, you misunderstood. Each cycle is a fixed amount. The cycle life is how many full cycles you will get over the life of the battery if you discharge to different levels. If you discharge to 80% you will get fewer total cycles. That chart shows that. An 80% discharge is .8 cycles. A 50% discharge is .5 cycles. But if you discharge to 50% you will have a lot more cycles over the life of the battery, as the chart shows. Its not how many 80% discharges you can get compared to how many 50% discharges, it explicitly defines the Depth of Discharge (DOD) for a cycle as 100%.
Here Lifelines Conclusion:
"To get the best cycle life, the average depth of discharge should be as low as possible. Concorde recommends the average depth of discharge be no greater than 50% of the battery’s 20 hour rating."
Ross
Earlier you said this
I think you read wrong. A battery cycle is always a 100% discharge, so 5 80% discharges is the same as 8 50% discharges, both are 4 battery cycles. You get more total power if you get more cycles.
Your earlier statement says that a cycle is any group of charge and discharge events that ADD UP TO 100%.
If you are reading the chart and then putting the add up to 100% on, at 20% DOD, you would have the 2800 "cycles" divided by 5, but that is not how Lifeline defines a cycle.
You have now added another term of "life cycle" which I assume you are saying is the total number of 100% added up single cycles a battery can produce. This is the same thing as what has been being called the "lifetime total energy storage before failure" or "lifetime battery capacity" and is calculated by taking the chart cycles at any given discharge depth and multiplying it by the amount of AH recovered (80AH for 100AH battery at 80% DOD).
20AH times 2800 cycles = 56,000AH lifetime
80AH times 550 cycles = 44,000AH lifetime
This is the 21% reduction that Yoshimura just mentioned
If you convert that to using cycles that add up to 100% but don't use varied cycle depths (which negates any advantage of doing this) you would get the following.
2800 cycles times .2 = 5600 added up cycles
550 cycles times .8 = 4400 added up cycles
You get the same numbers without the battery factored in so 21% change. So as soon as you start using the new term of "life cycle" and use it at a fixed DOD, you are saying exactly what I had said earlier, just different terms.
This discussion all started with the comments about a "cycle" being the added up, different DOD, individual discharge/charge events and that all "cycles" of that type are equal in the amount of battery degradation no matter what the various DODs are. That all of that type of cycle are equal is not correct, IMO, and that is what Markopolo originally was addressing in his post. The chart shows that, and you just also confirmed it with your own calculations albeit with different terms.
You said
Its not how many 80% discharges you can get compared to how many 50% discharges, it explicitly defines the Depth of Discharge (DOD) for a cycle as 100%.
The part about the number of discharges at any given % isn't important is what we have been saying, it is about how much total energy is returned at those discharge depths.
Please show us where it says anything explicitly about defining a DOD of a cycle as 100%. I don't see that anywhere except for when they do the AH rating at various discharge rates of 5,20, and 100 hours and there you have to discharge 100% to know how much power was in the battery (those ratings are also biased by Peukert which was discussed earlier).
What it all boils down to is that in the RV batter world a "cycle" is nearly universally considered a single discharge/recharge cycle of a any depth, as Yoshimura mentions. That is why the chart is made the way it is.
So bottom line is that, per your own explanation, you get more 100% added up cycles at lower DOD, which is true, but unless the DOD is consistent, you can't know how much it changes, so you are right at the same data a in the chart, but with different scaling. The only way I can think of to have an accurate calculation of life in the real world would be to take every discharge/charge cycle and use the chart to figure out it's effect on lfie. A single 80% discharge would use up 1/550th of the life, a 20% discharge would use 1/2800th of the life. When those numbers add up to 100% that life should be over if the chart is correct.
Of course, in the real world almost all of us are gong to do much more damage to our batteries from dumb mistakes like accidentally killing them dead too many times, so all of this is pretty mute.
One thing of particular interest is that per your quote, Lifeline says that they recommend that the AVERAGE discharge discharge depth should not be more than 50%. This is different than the traditional 50% rule that would make you believe that if you ever went below 50% the sky would fall. It also makes the entire understanding of battery management much easier for the masses, as it is pretty simple to understand. The inference, I think, is that if take the average DOD, you will get the number of cycles that the chart says, which is likely to be fairly close (probably within the 21% calculated at the 80/20 points), but not perfect. We have speculated on the forum in the past about if the average DOD would be the best and easiest to use tool to calculate what battery bank size is best for any given RV, rather than either counting on going all the 80% all the time or never under 50% DOD. My guess is that it is a pretty good indicator as long as you also have enough total capacity to get through a worst case happening.
