It's very straightforward with motordavid's writeup linked above, just have a 10mm and 13mm socket wrench handy... I suggest using an extension too. I replaced mine yesterday with a Bosch G49 from PepBoys for $99. It fit perfect and had the vent hole on the proper side already unlike the Werker he had to modify.

I didn't think accessing the battery was half as hard as some people made the chore out to be! All of the memory functions remained programmed aside from the OBC clock & parameters which were obviously reset.