As with any of these film cameras, you'd still want to use a small lightweight prime lens like Ultraprimes or Superspeeds and minimal AKS up front to achieve balance at the shoulder point with this new battery. Once you start putting even lightweight zooms and studio rods on the aforementioned film cameras, a 400' mag with film is not going to be enough counterbalance. So maybe they will make '1000' Mag' batteries next... :)
However, I have two questions:
1. Is the v-lock latching mechanism going to be strong enough to withstand the amount of torque that camera operators normally put on film mags without falling off? On sticks, a lot of operators like to grab the back of the mag to pan the camera, and with a battery in the same shape as a film magazine, the temptation will be greater to do this. Also, when operating handheld, mags can get banged around if an operator misjudges a door frame or has to run through a crowd.
2. How do you fly with such high capacity Li-Ion batteries? Do you guys have some new safety measures built-in to circumvent current TSA regulations?