Charging at well below-freezing temperatures

[kltye]

Earlier this week, my girlfriend took the MME out to the middle of nowhere Wisconsin for a work trip and charged the car outdoors with 120v. Now, the battery temperatures dropped to between 2F - 8F, but somehow managed to charge anyway. It did not appear to divert any power to warm up the batteries; it did charge to near 100% (from 39%) over the course of 40 hours. (I confirmed all of these values via OBD)

AFAIK, any type of lithium-based batteries are not supposed to be charged below freezing temps; doing so will immediately cause irreparable damage to the cells. Any idea how the MME is doing this? (I assume the BMS is smart enough not to do anything that even approaches hurting the battery pack)

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[Dnorwood98]

Earlier this week, my girlfriend took the MME out to the middle of nowhere Wisconsin for a work trip and charged the car outdoors with 120v. Now, the battery temperatures dropped to between 2F - 8F, but somehow managed to charge anyway. It did not appear to divert any power to warm up the batteries; it did charge to near 100% (from 39%) over the course of 40 hours. (I confirmed all of these values via OBD)

AFAIK, any type of lithium-based batteries are not supposed to be charged below freezing temps; doing so will immediately cause irreparable damage to the cells. Any idea how the MME is doing this? (I assume the BMS is smart enough not to do anything that even approaches hurting the battery pack)

I don't believe that 120V has enough energy to warm the battery. He has to be plugged into higher voltage. 120V only charges at about 3 mi/hour, so pretty minimal in terms of energy transfer.

 

[Maquis]

Batteries need to be charged at a slower rate when they’re extremely cold. So you have the perfect scenario for using a level 1.
Your numbers make sense - you added a little over 40 kwh in about 40 hours.

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