I use Energizer lithium metal batteries (not rechargeable Li ion batteries) in my equipment because they weigh so much less than other batteries. The motor grips in my both my 35 and my 645 take six batteries, plus my Sunpak 544 which also takes six. This makes for a huge difference in weight, especially when carrying multiple cameras. I noticed when I first switched over to Li that my motor drives were zippy as hell, though that could have been just the fact that the batteries were new. But I wanted to roughly test for any power difference, so I timed the recycle on my Sunpak when firing at full power, which was about 6 seconds. Then I loaded 6 new Duracell Ultra's into it and re-tested: 7.5-8 seconds.