Why Does the Range of an Ebike Battery Drop in Winter?

Ebike batteries are only humans as well. If it is very cold outside, they are not left unaffected. Something happens to them. The battery that recently supported you on, say, 80 kilometres without complaint, suddenly isn’t willing to do 60 kilometres any more. Why does the range of the ebike battery shorten in winter?

1. Basics of how an ebike battery works
2. What does a current flow slowed by cold mean for the ebike battery?
3. Old or new battery – does it make a difference?
4. How to store your ebike battery correctly in winter
5. Tips for riding an ebike in winter
6. Looking forward to better times?
7. Is a protective cover for an ebike battery worthwhile?

1. Basics of how an ebike battery works

If you want to know what triggers the frost in the battery, you have to remember – willy-nilly – your own school days. Physics and chemistry are in demand. Probably not everyone’s favourite subjects. The topic is: the electric circuit. When you hear terms like cathode as the designation for the negative pole and anode as the designation for the positive pole, it’ll certainly click. These two belong to a rechargeable battery. When discharging, positive lithium ions pass from the cathode to the anode so that electric current flows. During charging, the particles make a complete U-turn and move from the anode to the cathode.

Unfortunately, this does not happen in a vacuum. If it had, our cold problem would have been quickly solved. Instead, the process is linked to a medium, the electrolyte. This chemical solution is considered a well-kept trade secret by every battery manufacturer. What they have in common, however, is that they become increasingly sluggish as temperatures drop and change to a more viscous state. This makes it more difficult for the ions to move back and forth between the different poles. This tour de force causes the internal resistance of the battery to increase. Eventually, the current flow slows down and the battery loses performance.

The light blue area in the middle symbolises the electrolyte inside a lithium-ion battery. ©CC BY-NC-SA 2.0

In today’s ebike battery, the battery management system (BMS) ensures that this process does not continue ad infinitum. If there were no safety measures, the cold could even completely destroy the battery. You may be familiar with this from one smartphone or another. Similar systems are installed in them that initiate an automatic shutdown to prevent such a fiasco.

2. What does a current flow slowed by cold mean for the ebike battery?

Modern BMS therefore protect us and the battery from the worst. However, they cannot yet outsmart natural laws and the chemical and physical reactions that follow them. Consequently, a battery loses performance at temperatures of less than ten degrees Celsius, which in the case of the ebike translates into shorter ranges. We cannot tell you whether this is linear, exponential or whatever and what loss rates this leads to. As far as we know, there are still no scientifically sound studies that investigate how winter with frost and cold affects the battery on an ebike.

Studies on electric cars have shed some light on the subject. In January 2024, for example, the ADAC published the results of its own investigations. The corresponding article described how various electric cars were cooled down to a temperature of -7 °C for a test and then driven a standardised test track of 23 kilometres within 30 minutes. Due to the frosty conditions, the range of the electric cars dropped by an average of 40 per cent.

The effect of cold in winter on a battery is even more drastic in an analysis conducted by Geotab in 2023. The manufacturer of telematics solutions for vehicles examined anonymised data from 5.2 million journeys made by 4,200 electric vehicles. If the temperature dropped to -15 degrees Celsius, the vehicles lost 46 per cent of their rated range.

Yes, electric cars are not ebikes. Nevertheless, the studies show what standards you can expect. In this respect, it is relatively irrelevant whether we are talking about the effects of winter on an ebike battery from Bosch or another manufacturer. In an interview with the online edition of Alpin magazine, which is published by Olympia, an unnamed employee of bike manufacturer Scott stated that 75 per cent is the expected range of the battery in sub-zero temperatures. Compared to the analyses just mentioned, this value sounds rather optimistic. As mentioned, the BMS does react to cooler ambient temperatures and cooler battery temperatures. Normally, you can also see the result of the respective calculation on your display, so you can tend to believe the information. Even if the display may make you groan in frustration.

3. Old or new battery – does it make a difference?

Unsurprisingly, cold weather actually tends to cause problems for older ebike batteries in winter. There it is again, the human factor. Just like us, batteries also age. In addition to the sheer number of years, the number of charging cycles is particularly important. The older a battery is and the more often it has been fully charged and discharged, the more damage there is to its structure. This is another reason why the electrical voltage in an ebike battery can drop abruptly when frost sets in.

4. How to store your ebike battery correctly in winter

As is commonly known, the ideal temperature for lithium-ion batteries is around 20 degrees Celsius. So, the best thing to do is to treat your ebike to a holiday in a place with about this temperature over the winter. How about the Canary Islands, for example? For those who don’t want to or can’t get away, we have three rudimentary tips:

1. Charge the ebike battery at room temperature. Charging in the cold has been proven to damage lithium-ion batteries. When the battery comes in from the cold, allow it to acclimatise sufficiently and only then plug it into the charger.
2. If possible, store your battery in the ebike or separately overnight at temperatures between 15 and 25 degrees Celsius.
3. Avoid rapid changes between cold and warm. This may cause condensation to form in the battery. And the consequences that wetness can have for an electrical device certainly do not need to be explained to anyone at this point.

5. Tips for riding an ebike in winter

Apart from correct storage, you can make life easier for your ebike’s battery in the cold by adapting your riding behaviour. Two important factors in particular can be influenced: the handling of the e-drive and the equipment. Those whose battery is fully integrated into the ebike have a noticeable advantage from the outset. The frame acts a bit like a scarf. Not only does it keep the frost out better, it also ensures that the battery warms up more quickly during the ride. Apart from that, the following points are good for it:

1. While riding, warm up the ebike battery carefully when it is cold and thus slowly increase the operating temperature. Starting at the highest support level damages the battery cells.
2. Once the operating temperature has been reached, switch to a more powerful riding mode. This stabilises the operating temperature at a higher level.
3. Avoid short journeys immediately followed by long standstills.

Even if you take all these tips to heart, they will not eliminate all the challenges that cold weather poses for the ebike battery. What will remain, for example, is the enormous rolling resistance with which the snow slows down your progress in winter. Slippage in icy conditions also increases battery consumption. And if roads and paths are clear despite frosty temperatures, winter tyres will rob you of valuable watt hours due to their softer rubber compound or the integrated studs. However, this does benefit your riding safety.

6. Looking forward to better times?

Perhaps in a few years these tips will be superfluous. With the boom in e-cars, the winter suitability of lithium-ion batteries is naturally gaining in importance. In many corners of the world, research laboratories are running at full speed – and reporting initial successes. For example, employees of Jiatong University in Beijing and the Chinese Academy of Sciences have developed a rechargeable battery that can nevertheless access around 86 percent of its charging capacity at temperatures in the minus range. Researchers at the University of California San Diego have even gone one better. A prototype of their battery still has around 88 percent of its capacity at minus 40 degrees Celsius. One reason for the progress there is a new type of electrolyte based on a mix of dibutyl ether and lithium salt.

In addition, there is intensive research into rechargeable batteries with solid cell batteries. This technology replaces the liquid electrolyte with a solid one. This is expected to react less strongly to frost and cold. An ebike battery with a solid state cell would possibly work just as well in winter as in summer.

7. Is a protective cover for an ebike battery worthwhile?

It will be several years before such technologies appear in ebike batteries. Until then, you can give your bike’s battery an additional protective cover. Such covers made of neoprene are offered by both bicycle manufacturers themselves and specialists such as Berlin-based Fahrer. The principle of this insulation is very simple. While the motor is running and the battery is supplying the power needed for support, it warms up at the same time. This heat usually radiates unchecked into the environment and is thus lost from the point of view of the battery itself. With the neoprene cover in place, the ebike battery maintains a higher intrinsic temperature in winter, performs better and thus reduces the unavoidable loss of range.

How much benefit this warming winter garment offers is being diligently discussed in various forums and YouTube channels. Amidst the plethora of different opinions and experience reports, we believe we have identified the following four findings as relatively certain:

1. A protective cover allows the battery to cool down less quickly during and after the journey.
2. The temperature difference between riding with and without the cover is greater in lower support modes. In higher riding modes, the battery develops so much heat of its own that the effect of the cover is less noticeable.
3. At temperatures of minus five degrees Celsius and colder, the protective effect of the neoprene cover increases significantly.
4. If you have previously stored the cover and ebike battery at room temperature and only attach them to the ebike shortly before setting off, you will further increase the thermal protection.

With this in mind, always have a well-tempered ride.

Pictures: Bosch eBike Systems; retyre AS