Help needed batter/l85 madbull rail problem

[Commandoo]

Hi guys and girls.. I currently have this

http://i1297.photobucket.com/albums/...psbff03995.jpg

It's an ics l85 with a madbull rail.. I need advice on a battery, The problem I have is fitting a battery into the rail?? I went to a retailer today and they didn't have a clue. I tried an 7.4 lipo batt but at 1.100 mah (small stick type) it fits but is very tight and it's going to be gone in like 2 hours or so of game play.
I usally use a 8.4 volt 1600mah before the rail was fitted?
the battery is so tight in there I feel like I'm going to pull a wire out with it getting snagged.. Or twisted and brake the wire.

Any suggestions? With pics if possable..