Petrol under my NSR 125?

The fuel is likely to have pumped out of the carbs when you attempted to start it. A stuck float could also be the cause. As to the battery issue, did you put it back correctly. Negative to Negative (black) and positive to positive (red). If you did and the battery is charged then look for an in line fuse in the wiring to the battery and check and change it. If th ignition light comes on but the atatter does not turn then borrow some jump leads. Connect one to the negative terminal and the other end to the frame. Connect the other lead to the positive and using something like a screwdriver with a plastic or rubber handle, connect the other end to the screwdriver blade. Touch this onto the electric terminal by the starter motor. It should spark and turn over. If it does this then the solenoid has gone and you need to replace it. This is only a test method and should not be used to start the bike usually.