If it is illegal for merchants to scalp prices for batteries, building materials and gas at the pump because of the storm, WHY CAN'T THE OIL COMPANYS BE CHARGED FOR THE SAME THING!
Because the oil companies have to bring much of their supply from overseas. And if you cap the price, then Venezuela, the rest of OPEC, Russia, and all the other oil producers aren't going to sell oil to the US when they can sell it elsewhere and make more. It's called supply and demand. Mess with it and you get real shortages, depressions and famines.
If merchants don't raise prices, the resulting shortages of goods are apt to encourage hoarding. Rationing may mitigate the problem slightly, but some people may have a legitimate need for more than their ration while others who have no immediate need will still be inclined to take their ration for fear that future need may arise.
That having been said, it is unseemly for merchants to be seen as profiting from disasters such as this. What would happen if a merchant were to require customers purchasing scarce items to simultaneously make substantial donations to the Salvation Army (which the merchant would forward every hour or so on a regularly-scheduled basis)? This would ease the problems associated with price controls without making the merchant look like a bad guy.