Running total with upper and lower limit

I do have exactly the same issue on my desk for some months and I am unable to solve it in DAX so far. I will try to reexplain the issue and any help is highly appreciated:

The issue is about a battery storage for a wind power plant. We sell the energy to traders, but right now we must accept discounts, as we are not able to guarantee a predicted energy amount 24 hours in advance. There is always a difference, let's call it [delta], between the forecast and the real production. We intend to use batteries to reduce this difference. My task is to calculate the optimal size of these batteries. To do so, I must split the delta to the amount, which can be stored in the battery and the residual delta, for which we will have to pay a penalty. 

Example:

Let's asume the battery has a capacity of 5 and an initial state of charge [Battery_SOC] of 2,5, reflecting 50% charging. The following table shows the [Delta] between production and forecast. As long as the [Battery_SOC] is in the interval [0..5] the [Delta] is assigned to [Delta_Battery]. Any residual [Delta] is assigned to [Delta_Grid]. In consequence we get the following charging figures:

The calculation is easy in Excel, but given the extreme high numer of datapoints, the calculation must be performed in PowerBI (DAX or M). I am simply unable get the right code for Battery_SOC_BOP, which is always Battery_SOC_EOP from the periode before.

Thank you in advance for your support!!!