Battery preconditioning—or simply put, battery preheating—is critical before a DC fast charging session, especially in the cold season that we now have in the northern hemisphere.

Bringing the battery cells to the optimum temperature for charging will not only prolong their life but also help maximise range—which takes a big hit in the cold season—and shorten charging times.

Preconditioning the battery also ensures a safe charging session for your battery. Basically, this function will heat your battery pack to a temperature above freezing, allowing it to take a full amperage charge.

As a positive side effect, preconditioning the battery results in a warm cabin while the battery is getting warmed. Overall, there aren't any downsides about preconditioning your EV's battery, with the sole exception that you will pay the cost of the electricity needed to warm the battery despite the fact that none of it actually goes into the battery.

But don't take our word for it; a Tesla owner did a test to highlight the effects battery preconditioning—and especially its lack thereof—have on his Tesla Model Y's battery in cold weather.

The video posted on the It's Only Electric YouTube channel starts with a charging session at a V3 Supercharger with a preconditioned battery at 10 percent state of charge in -1° C weather.

The battery quickly started accepting current at a rate of up to 238 kW, and the session from 10% to 80% SoC lasted 33 minutes. The owner of this Model Y who lives in Sweden says his car normally would complete the same charging cycle in about 27 minutes, but seeing as this was a cold weather session, waiting an additional six minutes doesn't seem that bad.

Charging curve with battery preconditioning (grey) vs. charging curve with cold battery (green)

How will the same charging session go if the battery is not preconditioned, though? Well, the owner came back to the exact same charger two days later, after the car sat outside in freezing weather, to see the difference battery preconditioning makes.

This time, the outside temperature was -6° C, so a bit colder than the previous time, which might affect the result although the owner said the difference in temperature was not that big to have a meaningful influence.

After he plugged in the charger, it was obvious right away that the charge rate was increasing much more slowly than with a warm battery. The Tesla completed the 10-80% charging session in 42 minutes, which means it took almost 10 minutes more compared to the preconditioned battery test.

More importantly, the battery accepted charge at a rate of up to 135 kW, which was significantly lower than the 238 kW rate in the previous test.

Now, it's worth pointing out that the owner did not bring the car to the Supercharger ice cold the second time—he did warm the cabin beforehand to make the test as relevant as possible for a real-life scenario.

Comparing the charging curves is interesting as it reveals an almost flat curve for the cold battery and a descending curve for the preconditioned battery. Interestingly, the two sessions shared an almost identical curve from about 50% to 80% SoC; the big difference was during the first half of the session, when the preconditioned battery accepted charge at a much higher rate than the cold battery.

The conclusion is very clear: you should always precondition your battery pack before charging in winter if you want an efficient and quick charging session and if you care about the health of your battery. And if you're shopping for an EV, make sure it comes with battery preconditioning because not all models have this functionality.