From the New York Times
The 787’s cabin maintains a higher humidity level than other jets to increase passenger comfort. One theory is that the humidity could have created condensation that caused a short circuit in the battery or its wiring.
Another concern is that the composite skin absorbs more heat from the sun than the aluminum on other planes. That has prompted questions about whether the battery in the transmitter could have been degraded by excessive heat from the skin.
http://www.nytimes.com/2013/07/20/bu...-wire.html?hpw