The rules are clear but differ on international flights from domestic. Within the US (HI included) 311 liquids rule starts everything off, but you can check more eliquid in your luggage. You must bring everything in your carry one, charger included. I find a simple IMR batteries backpack bag with everything in it will suffice as separated for screening purposes. batteries should stay in regulated mods and better out of mechs. In all you should not bring more than 2 spare batteries. How you define that when you go with 4 mods with various battery needs is not outlined well but I find if I bring 3 extra batteries 2 dual battery mods, 1 triple and 1 single, the 3 spares will see me through the trip even if I have to shelf a mod. Battery differences like 20/21700 and 18650 mods add to the complication so use your best judgement and be ready to explain whatever to tea. Building tools under 5" are okay. To date, not a problem but typically a 5-10 minute delay every time