[moparts]

1st of all never take the pos. cable loose from a battery 1st. If you take the ground loose 1st and your wrench hits ground there is no sparks. If you take the pos. loose 1st and hit ground you have a arc welder.

Anything that stores voltage (condensor, possible radio capistors etc.) can cause a spark as you mentioned. Anything drawing any voltage at all (alternator, clock etc) can cause a spark when connecting battery back.