Hi wiedehopf,
I wish the official answers all agreed. From BEA
https://www.bea.aero/docspa/2010/f-p...k101208.en.pdf para 2.2
"Throwing water on a lithium battery fire can, however, revive the flames and make it more difficult to extinguish because of the reduction of lithium in water, which leads to the release of hydrogen, which is highly inflammable."
So it sounds something like if you don't have anything else better - then use water to cool the battery and extinguish the flames in the surrounding materials.