What mean circle with letter on scheme?
The connection between (A) and (B) is a current shunt. The amplifier DA1 senses the voltage difference between (A) and (B) to measure how much current is coming out (or going in) to the battery GB1.  That shunt could be a special trace on the circuit board. Or it could be a piece of wire as @Brian Drummond suggests. 

You cannot successfully copy this circuit without some knowledge of the resistance value of that shunt.  That information is not shown in this schematic diagram.