For starters, NEVER disconnect the battery from a car that is running - the battery forms part of the system the regulatse the voltages on the main systems and disconnecting the battery while the engine is running can result in voltage spikes that can damage many modules in the car, including the alternator.

I removed the negative terminal for 5seconds I don't think it has caused damage. But yeah I knew there was some slight risk.
I'm desperate to find the issue.