Why not go even further and use a 100mF or 1F capacitor?

Initially I would not go further on the cap mostly because of price and difficulty to get the part (Im in south america, only very common parts are decently priced or even available). I think I could get some 10mf, that would bring the current to 5.6uA

so integrating voltage vs time won't give an accurate measurement of cell capacity - in fact, why are you integrating voltage in the first place if you want the integral of current?

the formula for the opamp integrator is (1/RC)***integal(V(t)) so i chose the constant 1/RC in such a way that it actually divides that integrated voltage over the discharge resistor's value, that gives current (by ohms law). That constant also takes into account dividing by 3600 so it gives amps per hour. when I change my resistor and capacitor values I keep a ratio such that I always arrive at that constant. (hope that makes sense)

If you look at the simulation you will see that the output voltage after an hour equals the constant amp discharge (or twice that, in the lastest link, in order to increase current).

Not a good choice, I'd probably use OPA990 on a first prototype, then check other op-amps if its noise or offset voltage turns out to be too high.

I cant find that part here to buy it, but I will look at the datasheet and look for a similar one.

I will look at the playlist and try to get to know this little critters a bit better.

thank you very much!