I used to get irritated by these regulation, until my battery pack (that can use to charge phone) started to overheat and smoke while I was on the ground in an airport. It changed my prospective completely.

DO NOT BUY cheap Chinese battery packs. DO NOT BUY Duracell cell phone accessories and battery packs - they are not made by Duracell but license to a low-end accessories company in New York that uses the cheapest crap from China.