Taylor's Theorem for Quadratic Approximation

Given the function $f(x) = 7(1-e^{-0.7x})^2$ (inspired by Morse potential energy) we find the quadratic approximation, $Q(x)$, of the same at its minima. Let us call an approximation valid if the value of $f(x)$ differs from $Q(x)$ by less than $25\%$. Around where does the quadratic approximation first break down, for $x>0$?