The game will say you can't play it anymore and will give you a link to see what the full version is about. It also gives you a decision whether to delete the demo or not.
Currently, as of this moment, no.
as of right now, no
there is a demo section in the eShop and you can also use the search
No, but they will come out with one :)
you can't. But you can get a demo on nintendo dogs + cats on 3DS
Here: http://3dsmaxtrial.autodesk.com/3dsmax2008trial/Autodesk3dsMax2008_ESD_Trial.exe
Yes, they will cost money unless it is a demo or a limited time event
You can get the free demo, although that isn't the full game.
it clicks
Yes. The DSi, DSiXL, 3DS, and 3DS XL all have the same charger.
It won't fit in a DS or a DSi, there is a tab on the 3DS game to stop it.
The 3DS uses a proprietary battery made specially for it by Nintendo. Therefore the only battery it takes is a 'Nintendo 3DS' rechargable battery.