My guess is that there’s not enough of it to matter. In the Li-poly batteries, there is no metallic lithium, all is safely locked in the lattice of either the cathode or the anode. Which itself may burn, and the carbonate electrolyte is also flammable, but neither is especially dangerous. Check out various videos of intentional failures of Li-poly (and Li-ion, the metal housings give a little better visuals for the rapid spontaneous disassembly) cells and it is not the thermite-and-napalm-death that their reputation would suggest.
I’d guess that there are two concerns. The no-turbine-disintegration (or at least catching the torn-off blades) is the must, a degree of resilience against loss of functionality on ingestion of a bird of small to mid size is also desired.
