When I am finished with my iMac for the day, I put it in sleep mode, leaving the mouse and keyboard turned on. I use the mouse and keyboard heavily and after a month, the battery level on both is still showing 100%, so I don't think that leaving them on when the computer is sleeping will cause significant battery drain. I always use sleep mode and I don't think I have actually turned the computer off in the month I have had it, other than restarts when doing updates, etc.