trick behind removing the airbag is to have a small mirror, place it where the dials are and with a long flat-head screwdriver locate the clips (you will need to turn the steering wheel 90o either side to give access to the holes)
you don't need to unclip the battery but make sure all electrics are off, no ignition! the clips need to be pushed sideways and are sometimes forcefull. you will then need to unclip the airbag module and undo the nut in the middle of the steering wheel.
if you're just replacing the airbag you won't need to do that
P.S. try and get some light round the back too