NEVER!!!!!! Take out or put in the battery with a watch on . I have a nice scar around my wrist to show for this leason . LITT me up hooking up the hot side. watch grounded out on frame and poof... but the watch is still working . i take my batterys out of mowers and bikes and quads and tend them inside. Ohio winters have killed one two many even on a charger out side
Always disconnect the negative first and re-connect it last,avoids sparking and injury:s