Lithium battery test in winter

How much Polar or Arctic is actually in lithium batteries, which can be charged by a built-in heater even at temperatures far below 0 degrees Celsius? We have tested this for you, at least for one model.

Why do lithium ion batteries not like cold?

Lithium ion batteries are actually little divas, it must not be too warm, but also not too cold. Next to heat, cold is the second biggest enemy of rechargeable batteries. This is mainly due to the fact that at temperatures below freezing, the necessary electrochemical reactions take place more and more slowly and the internal resistance of the battery increases more and more. It is becoming more and more difficult for the lithium ions to do what they love, which is to migrate between the electrodes. This primarily reduces the battery performance. For example, if your battery lasts 10 hours at 20 degrees, it is not unusual that it is only 4 hours or even less at 0 degrees. The battery is no different from you in the cold; movements are also more difficult for you.

If you try to charge your lithium battery in sub-zero temperatures, damage will occur inside the battery, this is called “lithium plating”.

What happens during lithium plating ?

When charging the battery, our ions move from cathode (positive pole of the battery) to anode (negative pole of the battery). If we discharge our battery, it works the other way around, releasing electricity. If you now try to charge the battery when it is cold, the ions may not move from the cathode to the anode and store there as desired, but instead form metallic lithium. This lithium accumulates on the anode, thus “only” reducing the power of the battery in the best of the worst cases. However, it can also be really dangerous, due to the metallic lithium, a short circuit can occur, which can even lead to a fire.

For these reasons it is important that a lithium battery is only charged at plus degrees. As a rule, the battery’s BMS switches off the charging process at 0 degrees, thus protecting the cells from lithium plating.

The solution: a heating mat in the battery

To cope with the problem, battery manufacturers are increasingly installing heating mats in the battery housings. These heating mats are used to raise the temperature of the battery cells to values in the plus range if required, so that charging of the battery is possible even at outside temperatures well below freezing. So the theory 🫣

We tried the whole thing in Lapland at – 20 degrees.

In test the Supervolt 150Ah Polar

Supervolt provided us with the 150Ah Polar model for a test. And we can say at this point, it really was an absolute endurance test.

After an icy night in Finland, with temperatures of -20 degrees, the morning of truth had arrived. Will the battery start charging at these temperatures?

A look at the app showed a cell temperature of -12 degrees, and after starting the engine, the battery heater kicked in directly. So far so good, we thought. We set off for our next stop, but the temperatures were just too cold, despite the engine running, the battery didn’t get into the plus range even after more than two hours of driving, and it wasn’t charged one percent yet. Only after we had parked the car for a break, due to the congestion heat of the engine, the battery has become warm enough to be charged during the continuation of the journey, without this stop it would probably have been impossible. – 20 degrees is simply too much for this installation location. Thus, we could speculate that a normal lithium battery would also have performed the same service. Because here, too, the cells would probably have become warm enough due to the engine heat when stationary.

It has behaved differently at more moderate temperatures, our observations have shown that it works really well up to – 5 degrees with the heater.

Another situation is when you are on a campsite with electricity, there the battery heater starts immediately when reaching minus degrees and the cells do not even cool down so far.

You should keep that in mind if you want to be free standing in the winter and rely on cargo.

Here you can find the first Supervolt test: