I connected a bulb to a battery positive terminals with positive and negative terminals with negative .
It glows as it should but when i connect the positive terminal of the same bulb to the positive terminal of one battery and negative terminal of the same bulb to the negative terminal of another battery. The bulb does not glow.
What I want to ask here is that electric potential difference is being maintained then why does the bulb does not glow.
NOTE : Batteries are not connected with each other. Both batteries are separately placed.
It's the flow of a current that makes a bulb glow. In the second diagram there is no current flow because the current can't flow out of the end of the wires.
The following analogy may help. Electric current is like water flowing along a pipe. The wires correspond to the pipes. The end of a wire with air outside it corresponds to a pipe with a closed end because electric current can't flow out into the air (except a tiny bit which we are ignoring here). A battery corresponds to a device which creates pressure, allowing the water to be pushed up a slope to a higher level. Your second diagram is like a pipe running horizontally, then going up a slope, then horizontal again, then going up another slope. Both ends of the pipe are closed so there is no water flow.
@eqb is correct to some extent but the answer you want is as follows-
In a battery when electrons reach the positive end it triggers a reaction which causes "release" of electrons at the negative end, now as you have connected the ends of two separate batteries when you take electrons from battery 1 and give to battery 2's positive end the new electrons are released on the negative end of the battery 2 but the negative end of battery 1 does not produce any electrons as for that to happen the electrons have to reach the positive end of the battery first
So an equilibrium is reached so no more current flows
Note this is an extreme simplification but I believe this is better in this context as you just want the plain reason