Using your Canon 'BG-E13' battery grip. (Other Grips might also work similarly)
Turn your Battery Tray latch to the open/remove position
Place a sturdy rubber band around the battery tray to keep the tray from falling out
The battery is now disconnected....No battery drain whatsoever.
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I also now leave my camera switched on and use the battery tray latch as my on/off for everything.
After a few times using the 'latch as a switch, it becomes routine and always ready to take pictures
Turn your Battery Tray latch to the open/remove position
Place a sturdy rubber band around the battery tray to keep the tray from falling out
The battery is now disconnected....No battery drain whatsoever.
=========================
I also now leave my camera switched on and use the battery tray latch as my on/off for everything.
After a few times using the 'latch as a switch, it becomes routine and always ready to take pictures