I attached the positive terminal of my car battery with negative terminal and negative with positive terminal of UPS battery for charging for 1-2 seconds. After that I charged the battery with correct connection and the battery has charged. I checked the battery by direct connecting the air compressor to it and it is working fine. But my car has no electrical power at all and it is not starting.
What could be the possible reason for that. Because of lockdown I could not find the electrician please help me out.