Lithium Ion voltage during discharge
I created an equation for Vcell as a function of Amps (A) used and capacity [mAh] consumed.

The 3000 mAh rating at 0.2C means 0.2*3A=0.6A = 600mA for 5 hours or 11 Wh.

This degrades as Amps increase as shown in table.

Is that what you need?