E-bike battery in winter: range, charging and storage, maker by maker

Why a cold battery does not go as far

About 15% less range below 0 °C: that figure comes from the owner’s manual of the Booster Easy, a Yamaha e-bike [1]. The same table rates outside temperature as a factor of low significance, behind speed and gradient, both rated high. It is the only percentage we found in the manufacturers’ documents cited here. Bosch, Shimano and Bafang simply say that cold costs capacity or range [2, 3, 4]. ‘Below 0 °C’ is, admittedly, a generous category: -1 °C and -15 °C both qualify.

The reason is chemistry. In a lithium-ion battery, lithium ions travel from one electrode to the other through a liquid, the electrolyte. When it gets cold, explains the cell maker LG Energy Solution, that electrolyte becomes more viscous, the ions move more slowly and the internal resistanceThe electrical resistance inside the battery. The higher it is, the less voltage and energy reach the motor. rises [5]: the battery delivers less voltage and less energy.

The energy is usually not lost, just harder to get at. Once the temperature rises again, normal range returns, Yamaha says [6]; the ADFC, Germany’s national cycling club, describes a temporary loss of capacity [7]. Shimano adds a second effect: a battery charged at 5 °C or below goes less far on a full charge, and recovers its normal range once charged at room temperature [3]. So the cold strikes twice, when you ride and when you charge.

What a 500, 625 or 750 Wh battery gives you in miles and metres of climbing is set out in our calculation of e-MTB range. For a winter ride, I would rather knock a little off the result than hope for summer figures.

Riding in winter: keep the battery warm until you leave

In freezing weather, Bosch recommends taking the battery off after a ride, keeping it indoors and only refitting it just before the next one [2]. Bafang, Yamaha and the ADFC give the same advice [4, 6, 7]. A bike left outside overnight, by contrast, sets off with a chilled battery.

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For the ride itself, Bosch mentions a neoprene cover from specialist bike shops to protect the battery below freezing, and thermal covers for longer rides [2]; the ADFC also recommends a neoprene cover to limit the loss of capacity [7]. A cover does not heat anything, it only slows the cooling, so it does most for a battery fitted while still warm. Your bike shop will know which one fits your model.

How cold is too cold to ride? Here too, your own manual matters, because the limits differ. In its 2019 manual, Shimano gives an operating range of -10 to 50 °C for its batteries and warns that outside it, fire, injury or problems with operation may occur [3]. Bosch gives -5 to 40 °C for the PowerTube 750 [8]. At -8 °C, then, one battery is still within its range and the other already outside it.

The rest of the bike has its own winter rules, from lights to tyre pressure, and for you there is the three-layer system.

Charging: only once the battery is at room temperature

On charging, the makers agree in principle, if not on the numbers. Bosch, Shimano and Bafang set the lower limit at 0 °C and the upper limit at 40 °C, or 45 °C for Bafang [3, 4, 8]. Yamaha recommends 15 to 25 °C [1]. Bosch and Bafang explicitly advise room temperature [2, 4].

If the battery is too cold, the Bosch and Yamaha systems refuse to charge it. On Bosch’s PowerTube 750, three LEDs flash: disconnect the battery and let it reach the right temperature [8]. On a Yamaha, all four LEDs flash and charging restarts by itself once the battery is warm enough [1]. Bafang asks you to give the battery enough time to reach that temperature [4]. None of the four gives a time: it depends on how cold the battery got.

Why the caution? Charging a battery too aggressively at low temperatures can, according to LG Energy Solution, cause lithium platingMetallic lithium deposited on the anode during charging in the cold.: metallic lithium builds up on the anode, which shortens the battery’s life and may also affect its safety [5]. A campervan’s lithium battery likewise refuses to charge in the cold until it has warmed up, as our guide to campervans in winter explains.

Bafang gives another reason not to plug in an ice-cold battery the moment it reaches a warm sitting room: a sudden rise in temperature can cause condensation inside the battery, so the maker advises charging it where it is stored [4]. If you already keep it indoors, both problems are solved.

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Storing the battery for winter: charge level, place and checks

Winter storage is where the advice differs most. Here it is side by side, each with its source:

Let’s do the maths and lay the temperature ranges on top of each other: Bosch and Shimano recommend 10 to 20 °C, Yamaha 15 to 25 °C, and Bafang permits -10 to 35 °C [3, 4, 6, 8]. The only slice common to all four runs from 15 to 20 °C: a dry, rather cool room in the house. For the charge level there is no such overlap: Bosch stops at 60%, Shimano wants about 70%, Bafang 60 to 80% [3, 4, 8]. Here only your own battery’s manual decides, not another manufacturer’s.

Even within one brand, it pays to read closely. On paper, Bosch gives the PowerTube 750 a storage temperature of 10 to 40 °C, and in the text of the same manual 10 to 20 °C for optimum service life [8]. Its 2023 battery tips say 0 to 20 °C [9], its winter page 0 to 20 °C in dry conditions and 10 to 20 °C in damp ones [2]. Four documents, four ranges, and all of them include 10 to 20 °C.

What about the garage? Bosch mentions it explicitly in its tips, alongside the cellar, but at 0 to 20 °C and in well-ventilated rooms with smoke alarms [9]. The IFS, the loss-prevention institute of Germany’s public insurers, and the Verbraucherzentrale, Germany’s consumer advice centres, advise against an unheated or cold garage in winter [10, 11]. The two fit together: a garage that stays dry and frost-free meets Bosch’s condition, one where it freezes does not. A thermometer and a few cold nights will tell you which kind you have.

Should the battery stay on the bike? Bosch recommends taking it off for storage [8, 9], as do Yamaha and Bafang [1, 4]. Shimano allows the bike to be stored with the battery fitted, indoors at about 10 to 20 °C [3]. After the break, Shimano and Yamaha ask you to charge the battery before the first ride [1, 3]. The IFS singles out charging a battery that has gone unused for several months as particularly critical [10]: stay close by for that first charge.

What to avoid in winter

• Charging an ice-cold battery. Let it warm up first: below 0 °C, Bosch, Shimano and Bafang do not provide for charging anyway [3, 4, 8], and the London Fire Brigade puts it plainly: do not attempt to charge a frozen battery [12].
• Leaving it flat for months. Bosch warns that it can be damaged and lose a great deal of capacity despite its low self-discharge; Shimano advises charging a flat battery as soon as possible [3, 8].
• Storing it full or completely flat. Either way, Yamaha says, it deteriorates faster [6].
• Leaving it by a radiator or in the sun. Bosch advises storing batteries away from heat sources; Bafang notes that around 45 °C is common near radiators, in direct sun or in an overheated car, more than the 35 °C up to which it permits storage [4, 8].
• Leaving it on the charger for weeks. Bosch does not recommend it and advises unplugging the charger and battery once charging is complete [8, 9].

By car to a winter holiday

If the bike travels to the mountains on a rack, the battery rides inside the car. Bosch advises removing the battery and the on-board computer to avoid damage [8], the ADFC to keep the battery dry [7]. The IFS gives the winter reason: rain or road salt can cause internal short circuits and, at worst, a fire [10].

For a long journey, such as a holiday, Bosch recommends running the battery down to about 30% and only charging it fully on arrival [9]. Once there, the rule is the same as at home: overnight in the warm accommodation rather than in the cold car, and onto the charger only at room temperature. Legally, the journey is simple: according to Bosch, a private user may carry undamaged batteries by road without further requirements [8].

In winter, a battery follows one simple rule: it rides outside, lives inside, goes on the charger only at room temperature, and for every figure, it is your own battery’s manual that counts, not another manufacturer’s.

Julien de Jurquet

Campervans, motorhomes, cycling and calculators

Julien de Jurquet writes for Outfarer about campervans, motorhomes, cycling and calculators. He reads instruction manuals to the very end and never lets a figure through without its unit, so that your choices rest on sums rather than promises.

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