car battery rules

[ollydineen]

Why do most car manafactures say in the hand book and in haynes manuals when starting work say disconnect the NEGATIVE termonal only.Surley a disconnected battery is disconnected whatever way you do it .Confused.!!!!

[dougielogan]

There is less chance of a spark if you disconnect the negative terminal first, a charging battery gives off highly inflamable gases.

[Tim Baxter]

It depends on which pole of your battery is connected to the wiring (usually the insulated pole) of your car and which to the chassis.  It is safer to disconnect the non-chassis side of the battery as, if there is an accidental short circuit between any bare metal point on the car and the battery (maybe with a spanner), then no current will flow.  Probably better to disconnect both, though! (In my opinion)