f (0.88 + 8.965e^-1.44V)
= (0.88V + ((8.965e^-1.44V)/-1.44)
and
f(0.575+5.79e^-0.29V)
= 0.575V + ((5.79e^-0.29V)/-0.29)
In this case $\displaystyle V$ is a variable, not a constant. For the first integral, you should have written
$\displaystyle \int 0.88+8.965\exp(-1.44V)\,\mathrm{d}V=0.88V-\frac{8.965}{1.44}\exp(-1.44V)+C$
where $\displaystyle C$ is a constant.
No it doesn't matter since you're computing a definite integral.Will that matter in this: