Its pretty common that new batteries do not appear on the market immediately. You may find that some third party flash units and lenses have problems as well.
Just get a extra one of the old batteries, or rent them.
If you are planning to shoot 4K, your memory card may fill before the battery dies?? In any event, 4K uses a huge amount of power. Battery life will be very short when shooting 4K.
The old batteries have about 10% less capacity, I've seen lots of information posted. The main difference seems to be less FPS. Isn't the info in your owners manual??
Brian at "The Digital Picture" posted this.
Battery
The Canon EOS 1D X Mark II has a new battery and it warrants some discussion. The Canon LP-E19 battery pack has a 10% higher capacity (2700 mAh) than the LP-E4N being replaced. Both this battery and its LC-E19 charger share a red stripe and much of the battery is a different color for ease of identification – helpful since they appear very similar in design to what they are replacing.
Interesting is that this battery and the LP-E4N are forward and backward compatible, though the 1D X II's max frame rate drops by 2 fps when using an LP-E4N and the LP-E19 requires the LC-E19 for full charging. Learn more about the new battery at the CDLC here.
Battery life will vary with use and temperature, but the LC-E19 is rated for approx. 1,210 shots, up from the 1D X's 1,120 rating with LP-E4N batteries. I seldom needed a second battery to cover even a large event with the 1D X and ... a higher rating is even better (though the higher frame rate may equalize the difference in time duration).
The camera's battery menu informs of the type of battery in-use, the remaining % of capacity, the shutter count since last charge and the battery's recharge performance.
Read his entire review here:
http://www.the-digital-picture.com/Reviews/Canon-EOS-1D-X-Mark-II.aspx
