I would not put a battery ZTR in my barn if you want to have it (the barn) very long...
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Those fire fighters have obviously not been trained to handle LI battery fires
All you can do is spray WATER on them to try & keep them cool and prevent the fire spreading.
The battery will burn till it is all consumed and nothing on the planet can put it out.
The recommended emergency response is to simply keep water on it
If it is in a critical place then liquid nitrogen is used to smash everything and separate the + & - plates but they are still going to burn but it will happen quicker.
Note the mower just kept reigniting .
The red flames is the steel / paint / seat / tyres drive motors & plastic burning , ignited by the intense heat the battery gives off .
So all the fire fighters can do is keep the water up till the battery has been totally consumed to stop the fire spreading
Also note there was no way for them to get to the battery.
I hope JD at least put a quick release on the seat so it can be tipped up out of the way .
And just a word of warning, every gas given off by a burning Li battery is very toxic .
A lot of them give of HF which is fatal in very small doses and a very painful death as HF attacks your lungs effectivly dissolving them
It also gets into your bones .
Death is the ultimate conclusion and there is no treatment wat so ever so even if you are not seriously burned your life will be drastically shortened .