Seems like Line 6 deletes past posts.  I had posted the two button step to view the amp systems, including battery.  I'm not at home, so don't have it here with me (I think you hold Main and something else when you turn the amp on and it goes into analysis mode).  I'll check when I get home tonight and try to post the combo either tonight or tomorrow.

Changing the battery isn't a major deal.  You do have to de-solder the old and re-solder the new.  Line 6 repair should be able to send you the replacement free - they've sent me several over the years.  I've also gotten them from Digikey, but I've found discrepancies in the different models.  The biggest pain is reloading your user presets since they're saved in the battery.  If you are able to transfer setting via MIDI to and from the amp and your computer, great!  I was never able to get that sophisticated, so always have to hand enter the parameters (I at least had the foresight to have the values saved as hard copies).