The Li-POLY are dangerous! Boeing needs to learn this as well
The li-polymer batteries (with 3.6V voltage) are quite dangerous. They can burn or even explode. We strongly DISCOURAGE to use the li-ion (or li-poly) batteries in any kind of aviation applications.
We strongly recommend using the safe LiFePO4 cells that do not burn, do not explode and are thermally very stable.
More details about the Boeing battery incident
http://www.wired.com/autopia/2013/02/boeing-787-battery-flight-test/