How to cumulatively subtract in a specific range

Hello everybody, how can I adjust my for loop so that every time when the curve is above the max capacity and negative (see some examples, shown by the arrows), the values will be cumulatively subtracted by the capacity (see the black curve). With my Code I calculate only the difference at one point, with no effect on the actual capacity... You can find my code below.

C=cumsum(diffE,'omitnan'); % needed Capacity 
Cbmax= 1000; % in MWH, max. capacity of the battery storage
Cbmin= 100; % in MWh, deep charge border 

imax= C>=Cbmax-Cbmin; % find where C is larger than Cbmax
imin= C<=Cbmin-Cbmin; % find where C is smaller than Cbmin

C(imax) = Cbmax-Cbmin; % if C is larger than Cbmax: C=Cbmax
C(imin) = Cbmin-Cbmin; % if C is smaller than Cbmin: C=Cbmin 

Cres=cumsum(diffE,'omitnan');

for k=1:length(Cres)-1
    if Cres(k)>Cbmax
        if Cres(k)>Cres(k+1)
           C(k+1)=C(k)-(Cres(k)-Cres(k+1));      
        end
    end  

end