XTI won't turn off
I have a 350D and a 450D and both will go into power saving mode when not used for the prescribed period of time. I find there is virtually no loss of battery, even when left this way for days, and they are quicker on the draw when I see an unexpected opportunity for a picture. All I do is pull them out of my bag, or raise them up, and I am shooting without fumbling to make sure they are turned on.
And, in your situation it should eliminate the possibility of corrupting your memory because you shut down too soon.