I think one very very important parameter is missing here.

The price per Wh stored energy initially can be rather high but also irrellevant. If calculate only by that factor we wuld never get our money back unless we get the cells for free.

What actually most important if you ask me is the total number of Wh you get out of them before they are considered to be waste and goes to the bin

Calculating this can be done rather simple but also rather complex. I will do one very simple here just to show.

Lets say we have 10kWh of battery storage. This would be 900 cells if we went with 3Ah cells. Total cost if we buy them new around: 3EUR piece and that would be 3700EUR.

So thats 370Eur per kwh. Rather high price right? BUT...

Lets start to calculate on how much we gonna get out of the cells. And im just going to show 2 numbers taken out of my head and you could stretch this alot and with some proper math you can find the best point too.

Lets say we use around 80% of the capacity. At that range we know that we will get some where around 400 cycles of them and its stated that you in the end have somewhere around 60-70% capacity left. so basically the total Wh you get out of them would be:

400*0.8*0.85*10000 = 2710kWh. So now our price per stored kWh is around: 0,13EUR/kWh stored energy. And we still have some where around 60% capacity left...

Lets say we dont fully charge and we dont go to bottom? Ie lets say we use 60% DOD instead. And potentially get 1200 cycles with above cycles....

1200 * 0.6*0,85*10000 = 6120 kWh. And suddenly our price per kWh is down to : 0.06EUR per kWh.

But the problem with above is that on the first case you have max 8kWh useable and on the second only 6kWh.

So if you need to use the 10kWh you need to extend it a bit further. But at the same time it will hold a bit more cycles.

Above is just a very very very generic example and it can be done very very complex. There is very good docs on internet made on how to calculate this where the optimal is and what tht end cost would be but the forumals ar rather extensive. Above is just simplified based on them. I am trying to get some kind of webpage/excell done that can kind of do such graphs for ya but have not come that far yet. Because this is essential when you go into calculating how the cost will be and the durability on the setup built.

Sorry if it wasnt the original questions answer but i though this was needed here