Is it necessary to disconnect the battery when changing this sensor?

 

Reading thru this forum I ahve noticed similar probs with an 00 SL2. I shut the car off while on a closed hiway. When restarted and moving slowly with traffic the car began to boil over. I turned the heater on full which kept it from overheating and was fine once I was up to speed and out of traffic. Is this an resivoir cap or coolant temp sensor issue? Maybe both?