I'm just getting back to this thread but this seems odd to me. How the hell does the computer know how long the dive is going to be? I've never seen a computer that did anything more than warn you that battery life is not full. Granted, my experience of different computers is fairly limited.Dive computers will not let you start a dive they cannot complete, battery wise.
(also, backup compass?)
. fjp, if you are going to run a SPG without a console, you want a brass and glass one. The spg's that come with consoles, are usually plastic.