The graph above shows a decrease in SOC over time. A plot of battery capacity should show that the capacity is constant over time because the degradation model is disabled.
SAM models are two loss effects for Li-ion batteries that cause this decrease in SOC over time
First, internal resistance contributes to loss of charge over time.
Second, there are losses associated with voltage hysteresis resulting from the charge voltage being slightly higher than the discharge voltage: Given the same amount of power for charging and discharging, the charge current is lower than the discharge current, which causes the coulombs (energy) in the battery to decline over time due to heat losses and mechanical strain on the battery cells. This effect is modeled using the approach described in Tremblay, O.; Dessaint, L. (2009)
Experimental Validation of a Battery Dynamic Model for EV Applications
, World Electric Vehicle Journal Vol 3 No 2 289-298, and explained in this
University of Colorado - Colorado Springs course
.
To force the SOC to be more constant over time in SAM, you can set the cells internal resistance to zero. You could also try using the voltage table model instead of the Li-ion voltage model.
Best regards,
Paul.