There are various warning signs that a li-ion battery is about to fail and possibly catch fire. These include:
• A very hot device. Li-ion batteries generate some heat when charging, but if a battery is unusually hot to the touch, it could be defective.
• A bulging or deformed battery. If a battery is bulging or changing shape, it could be overheating.
• Battery making a noise. If you can hear hissing or crackling sounds, the battery is almost certainly dangerous.
• An unpleasant smell. Failing li-ion batteries can emit toxic fumes.
• Smoke. If a battery is smoking, a fire may have already started.
If you notice any of these signs, turn off power to the battery and – if it is safe to do so – move the device away from flammable items using an implement like tongs or a shovel. If a fire does start, call the fire service immediately.