Isolating the battery is the proper way to shutdown a device when no other method is available. It is also important to do this whenever disconnecting, or more importantly, connecting the LCD.
No touch when connecting a screen is usually just an improperly seated connector. Check the condition of the connectors, on both the logic board and the screen to insure they weren’t damaged. The screen artifacts you see are either a bad screen or an improperly connected one.
If the original, presumably cracked screen still works, try connecting it to see if the problem goes away.