Chassis and battery help

I'm upgrading my ultra saber and it seems the chassis disk won't fit my battery. I got the 7.4v 18650 battery pack and the CFX chassis disk. The disk has a very tight fit on the battery and is taking off the plastic covering from the battery. Any suggestions?

light sanding, the tolerances on the disks are pretty tight, so sometimes you need to sand it a little to widen the opening a bit to make installation easier. Just don't use too much force, acrylic is fragile.