they get recycle
No, it is not necessary to disconnect the batteries.
Establish which terminal is connected to ground and disconnect the wire from the terminal. Disconnect the terminal on the other battery that is connected to the load. Finally disconnect the loop between the batteries.
Car batteries are rechargeable storage batteries. They are designed to be constantly recharged.
Nothing will happen to the car if you disconnect the knock sensor. It just will not detect a problem if there happens to be one.
car batteries
DC definitely, all car batteries - all batteries.
a car battery that can be recharged. All automobile batteries are rechargeable.
BJ'S sells Excide car batteries.
dc
If working on the electrics of a car then it is a sensible precaution to disconnect the battery.
It's possible, if the batter is severly overcharged, but this rarely happens nowadays. Batteries are designed to prevent this.