Cycle life ?

Hey guys I was trying to do some calculations on number of cycles versus cost of the cells against money saved from what we dont draw from the grid.

The thing is all the info I can find says only about 500 to 600 cycles which would mean that for the money spent on new cells against the money not spent with your energy provider its cheaoer not to have the battery storage in the first place. :

Not it also would appear that they only rate the cells to end of life at 80% capacity. But of course they are still very worth while having at this point in their lives.

So what Im asking it does any one have a real idea how many cycles an 18650 could do if it was treated reasonable well.and by that I mean useful to us so still above 1500 mah.1000 cycles 2000 or more

Well, a cycle is one complete transition from fully charged to fully empty, 100% DoD. 500 or 600 cycles is a very typical figure for this and the cell will have 70% or 80% (or whatever %) capacity left, depeding on the manufacturer. If you don't go all the way up to 4.2V and down to 3.0V or 2.5V, i.e. do shallower cycles, then you can expect 1000 or even 2000 cycles. This effectively means one of your cycles is 0.x cycles from the manufacturers spec point of view. You trade maybe 20% usable capacity for bigger lifespan. I say lifespan, but the 70% or 80% rule still applies, so the cells aren't dead after that, but only lost about a quarter of their capacity. This is of course amplified by the amount of cells you use. The more cells you have in parallel the bigger your margin to play around with is.

This is why Teslas modules will last almost ages and are likely good for even more than 2000 cycles and probably something like 3000 cycles which they will most likely never reach during a normal cars life.

Long story short, if you are concerned about cycle life, and you probably are, run your cells between 4.0 and 3.2 or 3.1 Volt. That will improve cycle life dramatically. This is especially useful on cells that have been used already to prolong their 2nd life.

Long story short, if you are concerned about cycle life, and you probably are, run your cells between 4.0 and 3.2 or 3.1 Volt. That will improve cycle life dramatically. This is especially useful on cells that have been used already to prolong their 2nd life

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Exactly. In fact, by going from 4V - 3.2V as opposed to 4.2V - 2.8V increases cell cycle life into the thousands. Also, a cycle is not a low amount of capacity, it's closer to full capacity discharge/recharge. So, going from 2000mAh total down to 1300mAh and then recharge back up to 2000mAh is not a full cycle. So this helps to count towards the cells overall life expectancy.

We have a graph somewhere on here that shows it with quoted values. I just can't find it at the moment. But you can effectively increase to 3000 or more cycles by staying within the 4V - 3.2V range. You aren't loosing a whole lot of capacity by doing this. Maybe around 500mAh or so. Maybe less. And that's one of the major reasons for having so many cells in parallel, to help minimize cycling. That and to lower the amperage draw per cell by distributing it across them.

Battery University has some figures and graphs: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
Obviously these are just rough guidelines and estimations. You can still about double (or even triple) the given figures by using LiFe cells.

Ok so Im discharging to 3 volt and charging to 4.1 at the moment but once I have a few more batteries made and installed I will move to 3.1 volt and 4 volt. Also currently none of my cells should see any more than .7c draw and with more batteries made this will drop even more so that should help with the life span too.

Working on current electric cost of 15.070 pence per kWh and a cycle life of 2500 also reducing battery capacity from 5.1 to 4 kWh to save on life span and the cost of the new cells at 900.00 I think that works out at around 1500.00 saved over the life of the battery pack so a total saving of 600 so on that basis it is worth it.
But if the true cycle life was closer to the 500 cycles manufacturers quote it would end up cheaper to buy the electric from the grid.
I think battery storage is still very close as to weather its worth while in terms of cost and what you would pay if you never had it at all as in my estimations Ive not included all the other equipment and costs involved in setting up for battery storage. How ever energy costs are now starting to increase a lot so this will only improve things in our favour.
Before my electricity price went up in September we were paying 12.7 pence per kWh. Now its 15.070 pence which is a big increase

It is also the peace of mind that if/when the grid goes down, you wont be left without power. You could make the same argument about solar. It takes years to brreak even most of the time, especiallly professional installations.

Its not so bad for me as I get the feed in tarif.
Its government subsidised. So I get 14 pence for every kWh I produce weather I use it my self or export it to the grid. Then I get just over 7 pence for every kWh I export, but this is not metered, its just an assumed amount of 50% of what I generate. Then ofc there is the amount of electric Im not buying in from the grid as well.
Ive had my panels now for almost three years and it this rate they will have payed for them selves in 6 years max.
The feed in tariff lasts for 20 years so I should get 14 years of profit and even when its al finished I should still get most of my electric from the solar panels.
I use the money saved on my gas and electric as well as what I get payed to help reduce my mortgage.
And so far it seems to work out to just under 1000.00 a quarter so between 3500 and 4000 per year