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For temperatures between 0 F (-18 C) and 32 F (0 C), to what extent, if at all, should I insulate electric bicycle batteries?
I have read that they do not like temperature extremes.

  • Should I wrap a battery in 1 layer of bubble wrap during weather like this? Multiple layers? What about other types of insulation?
  • What amount of insulation will cause the battery to heat itself to optimum temperatures without overheating?

I realize that this depends on the temperature range, speed, and reliance on the battery when riding, so some sort of algorithm that takes all of these factors into account would be ideal, or at least some safe minimum amount, assuming the temperature is below freezing.

For clarification: I am talking about when the bike is being used outside during the winter. I intend to store it inside all the time when it is not in use.

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    ebike batteries already have a reasonable amount of built in insulation. There is likely 2 layers of plastic wrap (one around each cell, and one to form a pack) and finally a plastic outer casing. Assuming the battery starts warm (stored inside), then the current draw from the motor should keep it warm in use.
    – Andy P
    Jun 5, 2019 at 13:09
  • That would be the case if this were a single battery, but I should clarify that my bike has a dual battery setup, and the batteries alternate every 5 minutes, so they will cool off during their 5 minute break if not insulated. I've decided to make a neoprene cover for the triangle on my bike that will hopefully contain the heat from both batteries, confining it to the inside of the triangle, so we'll see how that goes.
    – kloddant
    Dec 5, 2019 at 23:29

3 Answers 3

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General advice is to store the battery at room temperature and install it in on the bike just before the ride. If the ride is under about 30 minutes the battery will stay warm enough not to be badly affected by the cold. For longer rides, a layer or two of insulation would not hurt (as long as it is not so much the battery over heats). Bubble wrap would be a great way to experiment and work out how much was needed and if it made a difference for your rides, but I would look at something a bit more durable in the form of an insulated zip up or Velcro cover for a long term solution.

When charging lithium batteries in cold climates you need to be careful. Never charge Lithium below about +5C. Ideally bring them up to room temperature before charging. Note this is the internal temperature of the battery - don't bring a battery that's been on a bike at -10C inside and start charging after a few minutes when the case feels warm, I would give it a couple of hours.

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  • Thanks for the advice! I've added the clarification above. It's good to know that bit about leaving the battery a couple hours to cool off - I would have probably given it just 1 hour otherwise, but a couple sounds much more conservative.
    – kloddant
    Jun 4, 2019 at 22:31
  • Great answer - want to add anything about condensation too ?
    – Criggie
    Jun 5, 2019 at 1:08
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    Discharging will warm the battery to some extent, so it's best to bring it indoors immediately after riding, rather than letting it cool down internally. This will give the warming a head start.
    – Chris H
    Jun 5, 2019 at 6:18
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    @ChrisH Charging will also heat up the battery. So it's always a good idea to bring it indoors.
    – Carel
    Jun 5, 2019 at 8:06
  • @Carel it certainly will, but my comment was in response to the 2nd paragraph in the answer: (don't start) to charge when cold.
    – Chris H
    Jun 5, 2019 at 8:22
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When charging at very low temperatures even once, lithium plating may occur that permanently damages the battery and may make it dangerous. But the temperature below that this occurs in both more serious sources I found was -20 °C or about (here, here), so should be really cold. And in this study they have done 12 charge and discharge cycles under -20 °C, the capacity dropped by somewat 20 % but nothing else is described.

High quality battery should have temperature sensor to prevent charging when the battery is too cold or too hot. Such sensors are mentioned in instructions of some power tools I have. Bosh E bike battery guide just gives recommendations but not strict requirements. I would only follow the manufacturer instructions.

Speaking about the ride, the internal battery heat and factory insulation may be enough or not enough, depending on the temperature and level of assist. From a longer standing bike the battery should probably be removed into some warmer place as it produces no heat when switched off, so no insulation can keep it warm.

These batteries should be charged reasonably away from the flammable environment. If you cannot find such a place, protection boxes are available (google for 'lipo guard').

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  • I wouldn't bet your house and your life on your battery having a good enough temperature sensor not to burn it down. Better advice is just to assume that your battery doesn't have a temperature sensor and just only charge it when you are sure it is at room temperature.
    – kloddant
    Jan 18 at 19:21
  • Find a place to charge the battery where it could burn with less danger.
    – nightrider
    Jan 18 at 20:43
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You can ride for 15 minutes in below-freezing weather without insulating the battery.

Parking your bike outside for an hour in that temperature will affect the battery and the bike will be sluggish.

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    Welcome to Bicycles SE. This site does not operate like a typical forum. It operates on a Q&A basis. Please only use the "answer" button to answer the OP's question. Once you have asked and answered a few questions, you'll have earned enough reputation to vote up questions and answers that you found helpful.
    – Criggie
    Jan 18 at 19:54
  • Strange, I have never observed such a thing with mine.
    – nightrider
    Jan 18 at 19:56
  • I have copyedited your text to bring out the answer more clearly.
    – Criggie
    Jan 19 at 5:03
  • @Criggie I think you went to far in that edit. It is more in a "citation needed" state. I think it should be made clear this is a single riders observation.
    – gschenk
    Jan 19 at 12:53

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