Charging in the cold deposits metallic lithium on the anode. Dendrites can pierce the separator and cause internal short circuits and thermal runaway. Most modern battery management systems block charging below 0 °C.
Among all winter precautions only one is a genuine safety line: do not charge a lithium ion battery below 0 °C. Reduced range, softer power and unstable displays are matters of user experience. Damage caused by charging in the cold is irreversible and can lead to thermal runaway. This rule should be repeated in handover, training, manuals and after-sales scripts.
The mechanism is straightforward. In normal charging, lithium ions intercalate into the layered graphite structure of the anode. Below 0 °C the intercalation kinetics slow markedly. Ions cannot enter the graphite fast enough and instead deposit as metallic lithium on the anode surface. This is lithium plating. Most of the plated lithium can no longer take part in the cycle, which directly removes active lithium and permanently reduces capacity.
What follows is more dangerous. Continued deposition grows dendrites, and once a dendrite pierces the separator an internal short circuit forms between the electrodes. The heat released by an internal short can trigger thermal runaway, visible as smoke, fire or violent combustion. Such events often occur during charging or some time afterwards, which makes unattended overnight charging indoors the scenario to avoid most.
The first engineering line of defence is the battery management system. Most modern systems include protection that blocks charging below 0 °C: when cell temperature falls under the threshold, the charging path is interrupted or the current is limited to zero until the pack warms up. When a dealer investigates a battery that will not charge, the first check should be ambient temperature, not the charger or the pack.
Protection should be understood as the last gate, not as a reason to hand the risk over to it. The correct procedure always remains bringing the battery indoors, letting it warm up and only then charging. QERYU calibrates low-temperature charging locks and current limits in the battery management system, marks the charging interface and the housing clearly, and supplies B2B partners with winter charging work instructions and training material. The aim is to turn this safety line into a daily action that can be executed, checked and traced, rather than a vague warning.