The battery graph is not opening for me, times out.
Another option might be to pick off 10 points from an average curve, and put that data into an array for a lookup table also.
If your lookup point is in between points, then do a simple linear interpolation, not likey to be too far off.
Otherwise, you need to monitor current flow (measure voltage across a shunt resistor typically) and pick a curve to use based on the recent current history you would have collected.