Our conclusion on the subject
An e-bike battery is best stored over winter in a dry, frost-free place and with a moderate charge level. A temperature of around 10 to 20 degrees Celsius is crucial, as are regular checks to ensure the battery does not become deeply discharged. In the case of permanently integrated batteries, the entire e-MTB needs to be stored in as sheltered a location as possible. Bicycle covers help protect against the weather, whilst thermal covers prevent the bike from cooling down whilst in use. Incidentally, when charging, a cold bike should always be dry and at room temperature first.
Summer is drawing to a close, but autumn is giving us a few more weeks’ reprieve. For many cyclists, however, the time is now drawing nearer when the bike will only be taken out of the cellar or garage now and then. It is precisely those cyclists who enjoyed a spin along their local trails after work during the summer who will now find the shorter days proving a problem. The battery, in turn, can suffer if temperatures remain below freezing for any length of time. The odd frosty night when the e-bike isn’t used is normally no big deal for a lithium-ion battery. What does cause problems, however, are prolonged sub-zero temperatures, damp, a very low charge level and charging whilst the battery is cold. For longer winter breaks, therefore, the rule is: store it in a dry place, avoid frost and check the charge level regularly.
Store the battery in a dry place, ideally at a temperature of 10 to 20 degrees
The ideal place to store an e-bike battery is a dry indoor space with a consistent temperature. Around 10 to 20 degrees Celsius is a good target range. A cold garage, a damp cellar or an open cycle shed are far less suitable for long-term storage.
Bosch, a manufacturer of e-bike motors, for example, recommends storing its batteries over the winter in a dry room at moderate temperatures, whilst Shimano recommends a cool indoor space at around 10 to 20 degrees Celsius.
Key tips for storage
- Choose a dry room that is, if possible, free from frost.
- Temperatures of around 10 to 20 degrees Celsius are ideal.
- Do not store the battery or bike near radiators or stoves.
- Also avoid direct sunlight and intense heat.
- Always observe the temperature specifications for the relevant drive.
Maintenance charge: 30 to 60 per cent is optimal
The battery does not need to be left on a continuous charge during the winter break. The charger should not be left connected for weeks on end. It is better to maintain a charge level of between 30 and 60 per cent. This avoids both storing the battery when it is fully charged and harmful deep discharge.
So, when it comes to e-bikes, ‘trickle charging’ does not mean leaving the battery plugged in all the time. Rather, it means keeping it within a safe range whilst you’re not using it. Bosch recommends 30 to 60 per cent, whilst Shimano recommends around 70 per cent. It’s also a good idea to check the display every one to two months.
Key tips on battery charge levels
- Store the battery with a charge level of between 30 and 60 per cent.
- Do not leave it to charge when it is not fully charged, nor when it is nearly flat.
- Check the charge level every one to two months.
- When the charge is between around 30 per cent and around 60 per cent, top up only up to that level.
- Do not leave the battery connected to the charger for long periods.
- Charge the battery fully before your first long spring journey at room temperature.
Keep contacts clean, dry and free from corrosion
Road salt, dirt and condensation can corrode the contacts on the battery mount, charging socket, display and connectors. Before the winter break, these areas should be clean and completely dry. Even if you cycle in winter and then do not use your e-bike again for a long time, you should ensure that all parts of the bike susceptible to corrosion are cleaned – this applies not only to the electronic components. For normal dirt, a dry, lint-free cloth is sufficient. For heavier build-up on the battery mount, charging socket, display and connectors, you can gently clean them using a cotton bud and a small amount of isopropyl alcohol.
Under no circumstances should you scratch the contact openings with a screwdriver, sandpaper or other sharp tools. Contact spray, Vaseline or lubricating grease should also only be used if the system manufacturer has expressly approved their use. Sealed covers on the battery compartment and charging socket provide additional protection against moisture.
Top tips for networking
- Check the contacts for dirt, salt and moisture before storing them.
- Gently remove any salt residue after driving in winter.
- Allow the battery compartment and charging socket to dry completely.
- Close the covers again after loading.
- Do not insert any metal objects into the contact sockets.
- If there is significant corrosion or loose connections, consult a specialist retailer.
Built-in battery: Protect the entire e-MTB
On many modern e-MTBs, the battery is permanently integrated into the down tube and cannot be removed by the owner. In this case, the whole bike must be kept in the best possible condition throughout the winter. In principle, the same rules apply to the complete bike as to the battery: Store it in a dry, cool, but not too cold place, with the battery at a low to medium charge level. If the e-bike has been stored at sub-zero temperatures, it should be allowed to ‘thaw’ in a room at a moderate temperature before charging.
If a fully integrated e-MTB cannot be stored in a temperature-controlled room, a dry garage is the best stopgap solution. An open cycle shed should only be a last resort. It is essential that the bike is protected from rain, snow, splashes and persistent damp.
Key tips for permanently integrated batteries
- If possible, park your bike in a dry garage or a locked shed.
- Check the charge level regularly, even during prolonged periods of inactivity.
- Do not charge a cold bike if it is not in the carport or in a frosty garage.
- Before charging, bring the entire e-MTB indoors to a dry place.
- If you see error messages or notice damp in the loading area, contact your specialist dealer.
Bicycle cover and thermal cover
A weatherproof, breathable bike cover can be a good idea. It protects your e-MTB from rain, snow and dust. Important: The bike must be dry before you cover it, otherwise moisture may build up underneath it.
Neoprene or thermal covers fitted to the down tube can help to slow down the cooling of the battery whilst riding. This can stabilise the available range slightly in cold weather. However, they are not suitable as a solution for months of outdoor storage. They do not generate heat and are no substitute for a frost-free room. Such covers are therefore recommended primarily for use whilst riding.
Top tips on covers and thermal sleeves
- Only use breathable bike covers.
- Never pack away a wet e-MTB.
- Thermal covers can be used for journeys in sub-zero temperatures, but not as a solution for winter storage.
- Always cover the charging socket and connections with the covers provided.
- Do not use heating mats, fan heaters or electric blankets on the frame or battery.
What should you do if your e-bike has been left out in the frost for a long time?
If the e-bike has been left standing for a long time at minus 10 degrees Celsius or colder, the battery won’t necessarily be damaged. However, its performance may drop significantly for a while. The biggest risk is charging it straight away whilst it is still cold.
This isn’t just an issue when there’s persistent frost in winter. Even in autumn, there’s often a big difference between day and night temperatures. During the day, your e-bike might still be parked in the sun, but at night it cools down significantly in the shed or carport. That’s why a cold bike should always be left to reach room temperature before charging. What you should not do, however, is take the e-bike straight from the frost into a hot boiler room, nor should you actively warm it up (for example, with a hairdryer).
Key tips following a severe frost
- Never charge the battery when it is very cold.
- Do not place the e-bike on or next to a direct source of heat.
- Allow the bike to acclimatise slowly in a dry indoor area.
- Only charge the battery when it is dry and at room temperature.
- In the event of damage, error messages or excessive heat, do not continue driving and contact your specialist dealer.
Josh Welz
Editor-in-Chief