Rechargeable batteries such as lithium-ion cells don’t like the cold. They contain electrolytes in a fluid form (typically lithium salt in solution) to transfer ions (chargecarrying particles) between the electrodes of the battery. When it’s cold, the ions slow down and can’t insert properly into the electrodes, so the battery can’t produce as much current before it runs down. If too much lithium is deposited on an electrode it can lead to a short circuit and even a fire. Thankfully modern batteries and chargers are smart enough to monitor their internal state to prevent this from happening. Some electric vehicles preheat their batteries to ensure optimal working temperature.
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