If, like me, you've been reading the comments over at Nikon Rumors, it's a common complaint that the D4 battery life is significantly reduced vs. the D3S. (2,600 shots/4,200 shots respectively). There has been some speculation (always fun) that this may have been due to the new Electrical Appliance and Material Safety Law in Japan, which was also the reason for the cessation of shipping the D300s and D700 in Japan (http://nikonrumors.com/2011/11/08/nikon-d700-d300s-and-other-products-no-longer-shipping-in-japan.aspx/).
Perhaps Canon, for whatever reasons, are running into the same problems as Nikon.
EDIT: Also, hi. First post. Long time lurker.
At 2600 images it's still twice what I got with the mk4, just saying...