A problem is being constructed. It has constraints. One constraint is named energyBalance .
The first line, optimconstr(N) says that a constraint with N parts is being constructed.
The assignment to energyBalance(1) says that the first constraint is that the first battery voltage must be a particular initial condition.
The assignment to energyBalance(2:N) says that the next N-1 constraints are that the battery voltages must decrease each time by Pbattv*dt .