My understanding is that it's not allowed (or at least you need special permissions) to fly in a passenger airplane with the type of 6s batteries the S900 requires since they are well above the 100Wh capacity.
Now, would that be an option to use pairs of wired 3S instead?
Any experience with this?

You want to contact the airlines to get a better understanding with what the policy is with these types of batteries. Why not contact them to see what their policy is?

So nobody ever flies with one of those bigger drones? DJI-Mark I know the regulation, I was mainly asking a technical question i.e. whether it is possible and practical to wire 3S batteries in series so as to remain under the 100Wh limit (this limit is the reason why the TB-50 for example is just below 100 at 97 something).