every time i went through tech when i had my battery moved they asked to see it.i think they pay a lot of attention to that since if it's loose in the engine bay,it could be a big hazard.if they don't see it in the engine bay,they want to know where it is.i just had a standard battery box from Jegs,with a vent tube going through a hole in the trunk floor.never had a problem passing with that.being that your car is a hatchback,they may be more strict sicne the battery is in the passenger compartment.i did have a tech guy question this once on my car since i don't technically have a "firewall" between the trunk and passenger area-just the back of the rear seat as opposed to a metal divider as found on many older cars.he did say though that he'd pass my setup either way.
how is yours not legal?if it's because it's not secured well,you may want to take care of that regardless-that thing will knock your head off in a wreck.
Chris