Parameter extraction using curve fitting toolbox

Hi everyone, I have Lithium battery voltage data (y) vs time (x), plotted it in curve fitting toolbox. My custom eqn is a0+a1*exp(b1*x)+a2*exp(b2*x). Does anyone know how to extract the parameters and to fit the curve perfectly ? Also please tell me how to set the start point and limits. I am using thevenin 2RC ckt. I would be great if someone could help me. Thanks in advance

[Rik]

Have you already looked at the documentation for fit? (simply type doc fit)

A perfect fit is very unlikely with measured data, because at least some degree of noise is to be expected. Sometimes this noise is so minimal that you won't notice, but it might still mathematically be there. That is the reason why fit also offers some statistical output about how well the data fits the model; the GOF (Goodness Of Fit).

Have a read here for some hints about where you may be able to find answers on your own.