Right then.
I have a G&G SCAR-L. It's ace. Ignore anyone that says you can fold the stock for CQB because 1) that's NOT why the stock folds and 2) it's a pain to try and use with the stock folded anyway.
If you buy the CQC version the gun comes with a barrel extender to the same length as the standard rifle. This can be easily unscrewed which then gives you the CQB length gun. Simples.
I run a 7.4v LiPo in mine ( this one in fact:
http://www.componentshop.co.uk/7-4v-2200mah-35c-lipo-battery.html ) and it's fine and dandy. It does NOT need a cranestock battery as the battery space is a big square block in the buttstock. The ONLY reservation I have is that it's quite easy to bend the pins the connect the main part of the gun to the battery holder, but it's easy to not f*ck it up - you just need to be a bit aware of what you're doing when you fit the battery.
You WILL need a downgrade spring though. When mine turned up it was shooting at the thick end of 400FPS! Get the shop to do it for you and aim to be under 340FPS as then you'll have no trouble with any of the sites you might want to use (CQB sites for example tend to be quite low on muzzle velocity).
Well worth the money and a gun that will last you a decent length of time too. Good choice.