I agree MMF that this could be a problem, but in practice it's almost impossible to get a refill when away from home, anyway. Getting avgas is the #1 job and then you look for a hotel
At really big airports it should be possible to refill using the facility for topping off the crew emergency oxygen in jets. I don't know anything about jets - I believe that in many transport jets types the bottle (located near the nosewheel) is actually swapped out but I know for sure that in King Airs the bottle is fixed (in the tail) and there is a threaded fitting for refilling. One could in principle carry a suitable adaptor. I looked into this once but was unable to borrow the other end so could not establish the thread. Anyway, this is pricey - I once paid £75 at Biggin and the bottle was away all day.