Got back from Vegas, and my 2007 MB GL450 has a dead battery, went to dealer, OUCH, came home, read instructions (have put in lots of batteries in my time) put in battery and NOTHING!  Rechecked what I did, re read manual, still nothing!  The courtesy lights, radio, and power seats work, but no headlights and the key will not turn in the ignition (yeah I jiggled the steering wheel).  Anybody with a MB out there with a clue?  I know it was a dead battery because I jumped it and it ran but since its got power everything I needed the new battery but once I put that in nothing!  A service tech at MB said I would have to reset the computer (?) I said what if I replaced the battery in the middle of the desert, how do I reset the computer there?  Ideas?

Turned out to be a loose fuse in the battery compartment, I'm glad it was something simple.

Thanks for posting the update!  I have a ML500 that will be due for battery replacements soon and I was hoping to be able to do this myself.

I spent too much in Vegas and wanted to save what I'm sure was going to be a good service charge for just a battery replacement.  The Gl 450 battery is under the passenger seat, not hard to get out but still requires a little more effort.  There's a bunch of different fuses in there and one must have been bumped and got loose.  The MB roadside assistance guy that came out found it and got it going again, no charge.

My battery is under the seat too.