The 1/u block is just the reciprocal: f(u) = 1/u.
The voltage-voltage block contains the non-linear function between SOC (state of charge) and output voltage.
It depends on the battery type - may be something like: 1.2 + 0.1*SOC - 0.01*SOC^2 etc...
Without accurate knowlegde of this block the model is useless.
P.S. Rts/Cts and Rtl/Ctl model short and long constant transients
It's a good paper. You can find most of the data that you need from the graphs!
For example you find: Rts, Cts, Rtl, Ctl, full charge Vout, etc...
Start with a first order model (Vout=4.1-alpha1*SOC) and find a good alpha1 from the simulations (match some discharge plot)...
HI hope you are well,
why do not use the model provided by Matlab, i do not understand why you are trying to develop your own model, see you can implement the simuklink model from the Matlab without being worried about the battery model,