I've taken a lithium quadra with head and spare battery on easyjet without a problem. Split the battery from the controller and removed the fuse from the slot back into it's storage holder, taped over contacts and I did the fuses just so they wouldn't fall out. Bagged each item separately in ziploc type plastic bags. Took all in carry-on luggage.
I also took the elinchrom manual and a printout of the test certification proving it was safe to fly with them. Didn't have a problem through security either way and it went straight through scanner without me having to open it. Case was 18kg and hand luggage 17kg as I'd got all camera gear in the bag - an aircraft spec Think Tank. Only had to put the macbook in my hold luggage as I didn't want it poking out the end of the outside pocket and letting the magpies take an interest...
When I went, my bag fitted in the sizes allowed but easyjet have since shrunk the sizes slightly where they'll guarantee it can go in the cabin with you. Things meeting the old spec may be put in the hold on busy flights as I read it.