Cold Cells, Changed Power | Crew Blo Marble Kiosk

Start with the temperature inside

A cold soak describes a period in which a battery exchanges heat with colder surroundings. It is not a guarantee that every cell has reached the same temperature. Large packs, sheltered compartments and recently operated equipment can retain heat unevenly. Record ambient temperature, several representative cell or module temperatures, rest time and recent current history. Without that context, two tests labelled “winter performance” may describe very different starting conditions.

In many lithium-ion cells, lower temperature slows ion transport through the electrolyte and active materials and changes the rates of electrode reactions. The resulting polarisation increases the difference between equilibrium voltage and terminal voltage under load. An equivalent resistance can help describe a particular test, but it is not a fixed material constant. Its apparent value changes with pulse duration, state of charge, temperature, cell design and the measurement method.

Power loss is not the same as lost inventory

When a load demands current, terminal voltage can fall to the battery-management system’s lower cutoff sooner than it would under warmer conditions. The delivered ampere-hours and watt-hours then decline, even though electrochemically stored charge remains. A lighter load or an approved warming step may make some of that energy accessible. Do not defeat the cutoff to recover it: the limit protects cells whose individual condition may be worse than the pack average.

Separate a reversible operating limitation from lasting degradation. A capacity check after controlled warming can help distinguish them, provided the comparison uses equivalent charge preparation, rest periods and discharge conditions. One low-temperature test cannot establish long-term ageing. Repeated cold operation, inappropriate charging, calendar ageing and mechanical damage may overlap. A credible report states the conditioning sequence and uncertainty instead of attributing every missing watt-hour to a single mechanism.

Discharge and charge ask different questions
Condition	During discharge	During charge
Cold transport	Greater voltage loss can restrict usable power and energy.	Slower insertion kinetics can restrict acceptable current.
Useful observation	Minimum cell voltage under the intended load.	Cell temperature, state of charge and the validated charge map.
Control response	Limit demand or condition the pack.	Reduce, delay or inhibit charging as specified.

Response / Separate the charging boundary

Why charging needs its own permission

For many lithium-ion cells with graphite-containing negative electrodes, charging at low temperature can favour metallic lithium deposition rather than insertion into the electrode structure. This lithium plating can consume cyclable lithium and create safety-relevant degradation. Its onset is not determined by air temperature alone. Current, state of charge, electrode design, ageing and local internal conditions all matter. A pack that can discharge safely is not automatically ready to accept charge.

Regenerative braking and charging from a renewable source are still charging. Their brief or variable character does not remove the need for limits. The controller should use a validated operating envelope and appropriate temperature sensing, with conservative handling of uncertain or faulty measurements. A warm casing or one warm sensor does not establish that the coldest cell has recovered. Likewise, a display reporting a comfortable average can conceal meaningful spatial differences.

Laboratory workbench with battery test leads and instrumentation used to investigate cell behaviour. — Laboratory measurements are only transferable when cell design, conditioning and test method are specified.

Read a curve before borrowing a claim

When comparing published curves, check whether they report energy, capacity, pulse power or impedance. Look for cell format, chemistry, sample count and temperature stabilisation method. IEC 62660-1 addresses performance testing of lithium-ion cells for electric road vehicles; ISO 12405-4 concerns performance testing of lithium-ion traction battery packs and systems. Neither title alone establishes suitability for a particular installation. USABC test procedures also provide useful vocabulary for controlled performance comparisons.

Research from Argonne National Laboratory and the National Renewable Energy Laboratory is valuable for understanding coupled electrochemical and thermal behaviour, but a laboratory result is not a substitute for supplier limits. Lead-acid and nickel-based batteries have their own cold-temperature constraints, and lithium-ion families differ internally. Even cells sharing a cathode label may use different electrodes, electrolytes and constructions. Avoid turning one chemistry comparison into an unrestricted rule.

The practical response is a recorded decision chain: establish the initial state, apply a representative duty, observe individual-cell limits and compare the outcome against a warm reference. Then assess whether load management, a changed charging schedule or thermal conditioning is justified. Keep the energy spent warming the pack in the same accounting boundary as the energy gained. The next briefing examines how insulation changes that balance without creating heat.

Research starting points

Argonne National Laboratory — battery materials and electrochemical research.
National Renewable Energy Laboratory — battery thermal management and systems research.
USCAR — access point for USABC battery testing information.

NEXT: THE INSULATION ENVELOPE