Good choice for the gun.
From what I hear, the wall chargers that come with the Dboys (same as the E1 SCAR) are terrible and ruin the battery. I would recommend a new battery (9.6v) and such. IDK what the biggest battery it will fit is though.
Cheapbatterypacks.com is an AMAZING place to purchase batteries.
For tightbores, OMD is correct. Prometheus is supposed to be very nice, but I love my Edgi barrel. You can choose the length and even bore size if you want. (6.02-6.04 etc) I went with the 6.01mm barrel. Despite what people say, 6.01mms will NOT jam if you get a "spec of dirt." Using TSD .25s in my SRC G36K with an Edgi 6.01mm TBB, I did not get a single jam and the gun was dirty. (AZ's dirt is very fine is like dust) I cleaned the barrel at home and is was BARELY dirty, even after skirmishing all day. People say brass scratches easier, which is true, but unless you are shooting metal walmart bbs through your gun, it will be fine.
As with any TBB, use high quality bbs, not walmart or sporting good store bbs.
If you decide to get an Edgi barrel, pick up a Systema bucking, and a SCS. (Shredder's Concave Spacer) The SCS is basically a perfected H nub and I like mine very much. According to the creator of the SCS, Guarder silicone and Systema buckings work the best with the SCS.
Can't go wrong with either brand, but I suggest Edgi because it performs very well and their CS is amazing.