2019 Leaf battery overheating

GerryAZ said:

I am serious--air flow over the battery case at highway speeds will dissipate some of the heat and reduce the temperature displayed by Leaf Spy if the battery is significantly hotter than ambient (such as from QC).

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GerryAZ said:

Since power required to maintain highway speed is much less than QC charging, the discharge current is not high and the internal I^2*R losses (and hence heat generated) are low.

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GerryAZ said:

The internal resistance of new (not significantly degraded) LEAF batteries is quite low. The internal resistance increases as the batteries deteriorate so 8-capacity-bar batteries will generate more heat during discharge from highway driving (and especially from QC charging) than 12-bar batteries, but the internal resistance of even an 8-bar battery is still relatively low.

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GerryAZ said:

If the battery is cool, then highway driving will increase battery temperature until it reaches an equilibrium temperature enough higher than ambient to cause heat transfer through the thermal resistance(s) between the cells and ambient equal to the heat generated internally. The battery cells together make a large thermal mass so that large mass heats and cools slowly, but the heat transfer is dependent upon the temperature differential between the cells and ambient. In normal day-to-day driving, the battery will cool while the car is parked overnight, but battery temperature will ratchet up during a long trip with multiple QC's because more heat is generated during each QC than dissipated by driving between QC's.

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