Air Bagging a 6 Volt Car

just asking her... dont beat me up to bad(im just one step above a monkey with a wrench, and this may get me demoted).... Could you install a 12v battery in the trunk and charge it by attaching it to a 6v to 12v convertor? like a trikle charge on a battery? You wouldnt be using the battery all the time so wouldnt it recharge?