Once a battery is in thermal runaway it will keep heating up, oxygen or no oxygen. Putting the battery in an oxygen-low environment would stop the flames but no

Once a battery is in thermal runaway it will keep heating up, oxygen or no oxygen. Putting the battery in an oxygen-low environment would stop the flames but not the heat. You'd still be sat there waiting for the batteries to be done reacting before you can reintroduce oxygen. Which is why firefighting battery fires is such an irksome thing. You can douse the battery and get the flames out, but hours to even days later the battery can have collected enough heat to reignite spontaneously.