Lithium battery performance in cold temperatures

By December 10, 2009July 7th, 2018Fitness

Many Optibike riders like to ride in cold weather, and some experience reduced battery performance as a result.  Here is an explanation why, and what can be done about it.  

Overview

The capacity of Lithium Ion batteries will decrease with colder temperatures. As the capacity decreases, the bike will run for shorter times and enter Safe Mode earlier. Run times can be extended on colder batteries by running in ECO Mode. If the battery is stored in a warm room and then ridden in colder temperatures, the battery capacity will be higher as the battery will warm itself during the ride.

Capacity Decreases at Colder Temperatures

The capacity of Lithium Ion batteries will decrease as the temperature of the battery decreases. The maximum run time is achieved at temperatures of 25C (normal room temperature). At 0C (32F) the capacity of the battery will be only 80% of the battery at 25C.  At a temperature of -20C, battery capacity will be decreased to 60% of a room temperature battery. See chart below.

lithium-battery-temperature-vs-capacity

Keep the Bike Indoors Prior to Riding for Peak Performance

For best riding results, store the bike in a warm area and then take it outside to ride. If the battery is stored at 25 C and then ridden in air that is 0C, the battery will heat up as it is used and this will prevent it from cooling off, preserving the capacity. The exact amount of cooling of the battery will depend on the outside air and speed the bike is ridden.  If the battery is left outside in 0C temperature and then ridden, the capacity will decrease to about 80%.

 A Colder Battery Will Enter Safe Mode Sooner

When riding with a cold battery, riders will encounter shorter runs times, and the bike will enter Safe Mode earlier. Safe Mode is entered when the battery reaches a certain lower voltage and over rides the capacity gauge.

If you find the bike going into Safe Mode on colder days, try riding in ECO Mode, which has a lower drain on battery and this will keep the voltage higher and keep the bike form entering Safe Mode.  Limiting acceleration and keeping the bike out of Boost Mode will also keep the bike out of Safe Mode.

Safe Mode Indication

Safe Mode has been entered when the Red LED on the headlight begins to flash. The power of the bike is reduced to less than 200 watts. Run Time in Safe Mode will vary from 2-10 minutes. Exact run time will depend on battery temperature and how old the battery is.

Reset From Safe Mode

If the bike does enter Safe Mode, early in cold riding, it can be reset by turning the bike Power Switch to off, waiting 10 seconds, and then turning  bike back on. Then ride the bike in ECO Mode and allow the battery to warm up.

 

6 Comments

  • Dan says:

    Just to clarify what I meant with the sarcastic comment. Nothing personal:

    “If I wanted to ride a 300W bike and not have a boost I would have bought a Giant twist. You guys need to fix this. ”

    If I charge my bike in the warm house and ride in the cold morning, it does just fine. Maybe once or twice t hit safe mode. However, charging inside on a regular basis is not convenient. I have charged in the cold (45-50) rode 10 miles on a park-ride commute, and then hit safe mode on the return at 12.5 miles. Even if I charge warm and ride, my bike sits in the cold all day and I catch a safe mode on the way back if RT is 40-45min+, and less than 20 miles.

    I guess my comment is based upon an expectation that a 20ahr battery on an Optibike will give me more than 20 miles in all temps, fast mode. (1hr/mile min) Additionally, with a 22+ mile commute (then a charge) for the cost of the bike, I expected top be able to ride FAST mode all the way (with active pedaling), and not have to switch to ECO. I don’t want to ride ECO mode per se at 300W. At that point, my Opti has the power of those other bikes.

    Still, the drop-to-safe is a nuisance, and that alone is worth a fix, IMO.

    Thanks for opening up on the issue and informing us all.

    moral: charge warm, ride long.

    Dan

  • Dan says:

    Gents-

    Opti said:
    The Optibike 850 is spec’d to run for 50 minutes in fast mode, that is the advertised run time stated on the website. Your Optibike runs for 55 minutes, and what exactly is the problem?

    Not problem with 55 min of run time, just a question about what is happening when the power seems to drop a little? It is not in SAFE mode when that happens. In the summer, I see SAFE mode after 75-80 minutes.

    Opti said:
    “If the battery is stored at 25 C and then ridden in air that is 0C, the battery will heat up as it is used and this will prevent it from cooling off, preserving the capacity. ”

    I am a little unclear about what you need to be fixed, the above quote is a solution.

    Ok, I see what you are saying is the solution. That does help, but not always. I have charged inside and rode to work at 40-45F and still seen a safe mode after 16 miles/45 min. If the capacity reduces due to the cold, then the LED should sequence to a solid red led more quickly, and then enter safe mode. My bike does not. It can go into safe mode from a blink yellow and occasionally a solid yellow. SHould that be fixed or an accepted surprise? The other unknown question is what constitutes an end-of-charge in your book? Is it going into safe mode? Or the reduced power I mentioned above?

    Opti said:
    Yes, the answer to your second question is indeed yes.

    I appreciate that direct affirmation! 🙂

  • opti says:

    Dan- The Optibike 850 is spec’d to run for 50 minutes in fast mode, that is the advertised run time stated on the website. Your Optibike runs for 55 minutes, and what exactly is the problem?

    Yes, the answer to your second question is indeed yes.

    “If the battery is stored at 25 C and then ridden in air that is 0C, the battery will heat up as it is used and this will prevent it from cooling off, preserving the capacity. ”

    I am a little unclear about what you need to be fixed, the above quote is a solution.

    Cheers back at ya,
    Craig

  • Dan says:

    Craig,

    After about 55 min of fast mode riding in moderate temps, I notice the power drops a bit. Is that programmed, or just the voltage level tailing off toward the end as your graphs suggest?

    Summary:
    So the cold lowers the battery voltage AND reduces it’s AHr capacity. When riding in FAST mode and boosting, the low voltage is further reduced, or “droops” during the high current demand, and can drop below a preset (and secret) threshold value, which switched the controls into SAFE mode. Correct?

    Opti said:
    If you find the bike going into Safe Mode on colder days, try riding in ECO Mode, which has a lower drain on battery and this will keep the voltage higher and keep the bike form entering Safe Mode. Limiting acceleration and keeping the bike out of Boost Mode will also keep the bike out of Safe Mode.

    If I wanted to ride a 300W bike and not have a boost I would have bought a Giant twist. You guys need to fix this. I’ll trust the answer to #2 is a YES.

    Cheers,
    Dan

  • opti says:

    Dan- Glad you liked it…this one was for you!

    Your answers (well, some of them):

    1) That is proprietary. Sorry.
    2) Also proprietary.
    3) There are alot of variables that can go into ride time, such as amount of boost, and temperature. We advertise a 50 minute run time for the 850w MBB in FAST mode. Seems like you are over that, even in cold weather. Looks good to me!

    Craig Taber
    Optibike

  • Dan says:

    Craig,

    Excellent technical stuff … great feedback for owners. Thanks!

    Some followup questions..when your tech guys get a chance:

    1. What is the voltage trip point that caused SAFE mode to be active?

    2. Does Opti have plans to modify software to allow temperature compensation, or does the voltage level need to be fixed?

    3. During the summer, I ran my Opti fast mode for 101 minutes before I hit Safe Mode. Now, at temps of 5-10C, I can trip into SAFE mode from 40-55minutes. If the capacity is reduced to 80% at 0C, then should I not see 101x.8 = 80 minutes of riding in the cold before safe mode? I am about half of that. Why?

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