Iam getting error when i run the battery RC model

variables(Access=private) i = { 0, 'A' }; % Current v = { 0, 'V' }; % Voltage Qe = {0,'A*hr'}; % Charge deficit

equations

        v == p.v - n.v;
        i == Qe.der;

i got the following error "Total size of differential equations does not match the total size of differential variables". Please help me.Thank you,