Parameter Estimation in Simulink

I have simulated a battery using a 2RC model in simulink.

I also have my experimentsl data which are from HPPC test for the whole SOC range of the battery(0-100%)

While I am using the parameter estimation app of simulink to get optimized values for R1, C1, R2, C2, and R0, I have several problems:

1. the result stronglt depends on the initial guess. How can I make sure that my initial guess is accurate enough to give the best final results?
2. While you repeat the estimation process with different initial guess, and different time steps, it gives you different set of data for R1 C1 and R2 C2. How can I konw which answer is accurate?