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Thread: Leaf cells had surprising voltage sag in the cold

              
   
   
  1. #1
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    Leaf cells had surprising voltage sag in the cold

    I took my bike out for both the first ride of the month and the first colder-weather ride of the year earlier this week. I hadn't charged to 100% SOC, since I was just using my bulk charger. By the time I reached my midway charge point (22 miles) the voltage sag was getting very worrying! I was really worried that somehow letting my bike sit for a month or so with about 30% SOC had caused some degradation or that I had a bad cell or something. I went for a 34 mi ride today to see if I had lost a bunch of capacity, and it does not appear that I have, but that the voltage is sagging a lot more than I am used to. The temperature was about 50°F on the first, worrying ride, and 65°F on today's diagnostic ride. Has anyone else experienced this? What do you all know about voltage sag in the cold?

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    Senior Member Hugues's Avatar
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    Never really rode with cold batteries so i can't say.

    But what was the temperature of the cells themselves ? any idea ? Because if the bike sleeps in the garage, it takes quite a while to cool down the inside of the cells.
    Regards from Switzerland
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    The bike is kept in an uninsulated garage, and had plenty of time to soak down to the cool temperatures. I don't have a direct reading, but I would expect the battery temperature to have been pretty close to ambient temps. In fact, the garage temperature is/was one thing that worried me- it gets awfully hot in there in summer and I was/am worried about my cell spending a lot of time in there at high temperatures. It's worried me enough to wonder about pulling the bike into the house in the summer time, or maybe making some kind of active cooling for the battery that can run while the bike is in storage.

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    Seņor Member podolefsky's Avatar
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    Cells will sag more in the cold, but it shouldn't be very noticeable until you get below 40F. You also lose capacity in the cold, so if you didn't notice capacity loss then it shouldn't be cold enough to cause much sag either.

    Sag is directly related to current draw, so to compare you'd need to know the sag at the same current when the cells were warm and cold.

    Storing at 30% is actually a good idea. 50% is typical, 30% should be fine. You just don't want to store cells above 90% SOC.
    - Noah Podolefsky -
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