If we consider the battery shown in figure 3.2, chemical action causes accumulation of positive and negative charges, these charges establish electrostatic field 
both inside and outside the battery. When the battery is under open circuited condition no current flows through it and the net force acting on the charges must be zero. Therefore,
......................(3.13)
Fig 3.3: Battery in Closed Circuit
When we have a closed circuit as shown in figure 3.3, we must have at all points
......................(3.14)