First, "d" is not a parameter. You need to change it to be a "local data" and give an initial value, e.g. 0.
The error message regarding "default transition" is puzzling. To me, it seems to be a new type of error related to a "default transition". My guess is this. The chart contains states, thus it is a "state chart", not a pure "flow chart". The "default transition" has to be guaranteed to reach a state. Your logic has various conditions and it is not guaranteed, thus the error.
The easiest fix is to insert a blank state between your default transion and your top junction. The model then simulates. Obviously, this blank state is reduntant. You might want to change your implementation. For example, move the condition for "Bat_cur" outside of the chart.
One more improvement, there is no need to fill the "[Bat_vol>=Bat_vol_max]" condition. Leave it empty.
You don't need to write this code
if a>0
...
elseif a<=0
...
end
Instead, you can write
if a>0
...
else
...
end
