It's been a while since I've tested this, but I'm 99% certain the batteries won't drain if you correctly power down the unit and only drain when left in stand-by mode. Make sure you turn the unit completely off and then use the "hold" switch on the top of the unit.
From a best practice perspective:
- Not using internal AAs is incredibly risky
- They shouldn't be left in the unit for extended periods of time, but if it means you're too lazy/busy to replace them... leave them in.
You need to be using AAs. If you don't and lose power, you are basically fucked and your files will not be recoverable. Just because an external battery has adequate capacity (perhaps many times over) does not safeguard you from losing power. Bags get bumped an power cables can get yanked. Imagine a wook spills a beer on your bag and you are frantically trying to clean up the mess? Think you can do this without accidentally yanking the power cord? How about if the DC Input jack becomes loose? Mine is and if I wiggle it just right, it will cut over to internal AA power. Power failure can occur in many ways and it's suicide not to use the internals when the unit won't finish writing to the SD Card.
As far as leaving in batteries between shows, yes... you should remove them when applicable. Not going to a show for a week or longer? Probably best to remove them. Have a show in a few days? Don't even bother... leave everything in your gear bag and just make sure to properly power down the unit w/ the hold switch.
At the end of the day, this is a $400 recorder. The batteries probably aren't going to leak in a week and if they do, it's easily replaced technology.