Coming back to this thread six months or so later...
Ramon, the slop was pretty wild when you had more than two stacked. Even a one or two piggybacked would turn off most if not all operators, unless you can cope with stuff moving around on your sled. Mind you, as I mentioned, this was noted at NAB when properly over a thousand people had laid their mitts on this stack of batteries and was pushing it around. Even so, the casing material did not seem to be particularly hard. Not sure if a velcro wedge would do the trick. The slop gets worse over time. I checked out the stack of batteries several times over the 2 days I was on the NAB floor and the movement got noticeably worse.
It's a great concept, the idea of being able to stack batteries to charge which is one of the primary intents of this design but I wouldn't stack them on a steadicam sled, no way. Having said that the operators I know are disciplined in charging their batteries so I am not sure if many here would be taken by the stacking concept other than extenuating circumstances.
Clemens, you probably would have the ability to see these batteries demoed at a trade show in Europe in the near future. I also think PAG has some demonstration videos up if you are keen on this product.