Join Date: Jul 2000
Location: Panama City, FL
From a purely electrical point of view, it doesn't matter which side of the battery becomes disconnected first. Either side may elicit a spark upon reconnection, however, if sufficient current draw in the circuit is used.
From a practical standpoint, you should always remove the negative side first, which reduces the risk of completing a short circuit by a wrench, hammer, or screwdriver that accidentally touches both the chassis and the battery + terminal. There is no other reason to do it this way. It is simply a matter of risk reduction.
'Electrical Guru: Let me Check Your Shorts! Ooops...that didn't turn out right.