A regular battery should be vented if placed in the trunk or hatch area of a car. According to NHRA rules, which are created for 'crash conditions' of a vehicle, you would need a firewall between the passenger compartment and a battery placed in a battery box. I would recommend, if you were to put a battery in the passenger area, you should used a sealed one such as an Optima or look into a Gel Cell. Maybe Holley's (Reactor's) mini sealed battery. It's about the size of a motorcycle battery but puts out the same amount of power of a regular size battery.