RE: Are Lipos allowed on airline flights?
Actually, Federal Aviation Regulation 175 covers this subject. However, it is tedious reading. All the airlines have to comply with this regulation. Airlines are then allowed to set forth their policies as long as they comply with the FAR. If the FAR says it OK to ship an item, an airline may still have a policy not to ship. You might call Fedex and ask them, they know.
Carry on baggage is no different from shipping in the belly of the aircraft. In reality, the airline will not know what you have unless you raise the issue.
Violating FAR 175 will result in a Civil Penalty ($$$$$$$$$$$$$).
Someone mentioned cell phones having LiPos. The FAR states quantities or sizes of items. It might be OK to have 25 bullets for a hunting trip but not 100. Just an example.
Wet cell batteries are a no-no.
Hope this helps. At least now you have a better idea of what the rules are and can make your own personal decisions.