My 2008 Z06 battery died about two years ago due to lack of driving. I am retired and although I teach engineering, I don't drive the Vette enough. Winter in Colorado really challenged that battery. But I took it out (after considerable effort -- I now have a checklist) and had it recharged. When I started the car the clock in the GPS screen was blank. The box was there, but no numbers. My windows did not come up all they way, but the dealer showed me how to fix that: press up both window buttons up at the same time until the windows close completely. Now that the Satan Bug is keeping all inside (I am at high risk at 72), I did not turn over the engine enough in the summer and the battery died again. I took it out, recharged, back in, and windows fixed; and suddenly the clock is back up and working. I was surprised since I found that GM said that loosing the clock was a problem they did not have a cause or a fix; and would not fix anyway. I don't claim this is a fix, but if you loose the clock, disconnecting the battery for some time MIGHT do the trick.