You won't get a 9.6V NiMH nunchuck into that PEQ15. For a PEQ2, the 9.6V cells are arranged in a square configuration to fit it.
I run mini 11.1V and 7.4V square shaped Lipo in my PEQ15. Because the packs are only 1300mAH, just carry a second one on your vest. The nice thing about the PEQ15 is it puts very light weight on your front end and a quick change if needed since it is external.
Don't recommend a PEQ2. Take your current 9.6V and strap it to the front end and try shooting with it for the day then you'll see that the PEQ15 makes more sense.
There is a PEQ15 here with 9.6V NiMH but 1400mAH arranged in a 3x3 setup.
http://www.airsoftparts.ca/store2/im...bc-04-DE_2.jpg