In (1):  and  respectively

In (1): 

and 
respectively are rates of charge and
self-discharge at time t, whereas 

and 
denote,
respectively, number of charging EVs and inactive (that is,
connected but not charging) EVs at time t. 

and

are stochastic variables that could be modeled via
time-series techniques, whereas the uncertainty associated
with 

and 
could be taken into account via ranges of
variation.