There is a belief that colder temperatures drain a battery faster. That assumption isn’t quite right — chemical reactions slow in the cold, so the battery, much like food kept in a fridge, loses its active properties more slowly than in heat.
In itself, capacity doesn’t vanish in the cold. Car owners often warm a frozen battery in a warm bath and find that after such a treatment the battery “wakes up” and the starter turns the engine over with vigor without needing extra charging.
And the number of energy consumers in winter isn’t dramatically higher than in summer. In hot, humid weather you also run the electric window heater, push the heating fan to high speed, and the engine cooling system’s big electric fan can come on to prevent overheating. Add wipers and headlights to the bill, and the energy draw is similar to winter.
Heated seats and a heated steering wheel sip energy too, but they don’t work constantly. They run intermittently, which keeps their overall impact on demand relatively modest.
So why do batteries fail more often in winter?
Oil thickens in the cold and requires more energy during start. The generator, however, must compensate quickly for these losses — and that is where the core winter difference lies.
Don’t expect returns
The generator hums along and produces power, yet the battery may not charge as expected.
The reason lies in the battery’s internal resistance, which depends on many factors, including temperature. Ohm’s law applies here: higher resistance means lower current.
Consequently, charging characteristics at 20 °C and at −40 °C differ dramatically.
In practice, this means that lower temperatures curb the ability of an acid battery to charge. And that isn’t something you can change — it’s a design characteristic.
Amps and degrees
For readers seeking concrete numbers, here are results from a controlled experiment.
Several fully charged batteries of a common size (278 × 175 × 190 mm), with different technologies — AGM, EFB and standard lead-acid — were used. They were discharged partially to avoid damage from severe frost, holding a voltage around 12.24 V. The batteries were charged and discharged back to 12.24 V before being kept at room temperature.
When the temperature dropped to minus 30 °C, the charging currents ranged from 0.7 to 1.6 A, about ten times lower than at room temperature.
QED
The dependence of the battery charging current on the temperature
| Topla AGM Stop-n-Go 70R 760 a | Beer EFB 75 Ah 750 A | Tyumen Battery Standard 75 Ah 660 a | |
| Charging current at 20 °C | 29.0 A | 28.0A | 28.0A |
| Charging current at 0 °C | 7.1 A | 7.0 A | 7.0A |
| Charging current at −10 °C | 3.9 A | 3.8A | 4.0 A |
| Charging current at −30 °C | 0.7A | 1.5A | 1.6A |
Theory and practice
In practical terms, drawing hundreds of amps during cold starts and tens of amps otherwise yields only meager energy returns for a long period.
During long drives, as the engine compartment warms up, the charging current increases and the battery can replenish the energy lost earlier.
Short trips leave the battery with little opportunity to recover, and this is especially true for batteries located in open spaces such as many vans.
But what about?
If engine-compartment insulation is desired, use purpose-made thermal blankets rather than makeshift coverings like an old, loose quilt — improvised coverings can pose a fire risk.
To avoid the problems outlined above, it is wise to take longer trips occasionally to ensure the battery warms and recharges.
In regions with prolonged severe frost, insulating the engine bay can help the temperature rise more quickly, allowing the battery to warm and begin charging sooner.
When installed on the frame, periodic charging from a stationary source remains important.
However, a thermal cover for the battery does not solve this problem. It helps in hot weather but can hinder winter performance by slowing the battery’s heat buildup.
- How to properly light a car – a complete guide.
- “Drive” can now be read in Telegram.