To quote the PDF instructions:
"The battery should be charged in a spacious environment, staying away from high temperature, high humidity, and too close to the fire. Because the battery and the charger are electronic products, high temperature, and humidity will corrode electronic components, resulting in some harmful gasses and soot, and even a possible explosion to the wound". [bold emphasis added by me]
I don't know about you, Kathy, but that last sentence would give me pause.