Carbon buildup due to trigger arcing will happen even if you do use a shitty 8.4v Ni-cad battery. It's not a matter of if but when if you run w/o a MOSFET.The first upgrade I do to all my AEGs is install a MOSFET. Eliminated arcing and better trigger response makes this a no brainer upgrade. Extremely high quality Polish MOSFETS can be had for cheap!
http://www.wgcshop.com/wgc2008/main/...=mosfet%20gate (Just avoid the pico ones, they're not as durable as the standard ones) If you don't know how to solder, then now is a great time to learn.