haha ya science can work wonders, but really a car battery unfortunately wont work. you would need like 5 or 6 car batteries all pooling their power to use the lights, and even then it would only power the lights for a few minutes before they would need to be recharged. best bet for the shack is either a generator or running an extension cord to there from your house, possibly buried under the dirt? if you go with that option just make sure you dont forget its there in the future, and accidently cut it with a shovel though lol. while its plugged in. cuz that would kill you lol. however if running a cord is not a suitable option for you, id just go with that outside spot you got planned, so long as they arent on your property and no one sees you tending to them and you dont leave any convicting evidence at your grow site, even if somone does find them there is no way you could get in trouble. ya listen to what that other guy said about having a few different spots that way if one gets compromised you still have backups. i think i will be doing a few grows in different spots around my small town as well, just to increase my harvest ratio, (i am growing a few indoors right now) but if they get jacked it wont really suck too much you know? good luck man, hope it all works out for you!