In a word, its just not worth it! Most buyers who bought into generic battery pack got their rude wake-up call when it refuses to charge while some only worked on a specific model of a camera. Yes, it may look and give buyer a kick into thinking they saved, but only a fraction of my friends who did so was rewarded.
Moreover, its a $1400 machine...why risk saving $20 on a generic battery? Nevertheless, the better known OEM battery manufacturer include Camera Devices and Adorama.